Bio 108 Test 3

Monosomy X- Turner Syndrome

- 1 : 2,500 female births and is the only known viable monosomy in humans. - XO individuals are phenotypically "female," but do not develop mature sex organs. - Estrogen replacement therapy usually prescribed. - Typically does not cause learning disabilities.

Fruits

- A fruit is formed when the ovary wall thickens and matures. - Fruits protect seeds and aid in their dispersal. - Mature fruits can be either fleshy or dry

Reproduction in Animals

- A population can only survive by reproducing - Animals reproduce sexually and asexually, in a massive variety of ways. - Some species have no biological sex, others can change between them.

XYY

- About 1 of every 1,000 males is born with an extra Y chromosome (XYY). - Typical sexual development. - Do not exhibit any well-defined syndrome, but tend to be taller than average. - This may be due to the Y chromosome's relatively low amount of non- sex related genetic information.

Seed Development

- After double fertilization, each ovule develops into a seed. - Meanwhile, the ovary develops into a fruit, which encloses the seeds and aids in their dispersal by wind or animals. - Eudicot: two cotyledons - Monocot: one cotyledon

Sperm Delivery by Pollen Tubes

- After pollen is released, it may come in contact with a stigma. - This is pollination. - The pollen absorbs water, and germinates by forming a pollen tube. - The generative cell divides into two sperm cells. - The sperm discharge from the tube into the embryo sac.

Day 8 Summary

- Allopatric speciation: gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations - Sympatric speciation: Populations may experience speciation within the same geographical area. - Biological species concept: defines as species by what organisms it can interbreed with. - Morphological species concept: defines a species by structural features - Ecological species concept: defines a species in terms of its ecological niche

Summary Day 5

- Alterations in chromosomes often lead to disorders. - However, occasionally in evolution, chromosome alteration is advantageous. - Gene families may duplicate, shuffle, and evolve to produce new proteins, or to make variations on known proteins. - Usually these changes are detrimental, but rarely they provide an advantage.

Day 7 Summary

- Angiosperms have a very unique method of reproduction. - Plants have sporophyte and gametophytes generations, but in angiosperms they have essentially fused into a single organism. - They have coevolved complex relationships with many organisms to pollinate them or spread their seeds for them.

Day 6 Summary

- Animals have incredibly diverse reproduction strategies. - Sexual reproduction increases genetic diversity, although there are tradeoffs in energy expenditure and mate finding. - Some strange traits evolve via sexual selection, which may be fitness proxies.

Chromosome Theory of Inheritance

- Around 1902 = the chromosome theory of inheritance. - Mendelian genes have specific loci (positions) along chromosomes. - Chromosomes undergo segregation and independent assortment. - It wasn't fully understood that DNA itself was the "transforming principle" until 1944 (Avery et al.) - Before that, DNA was largely thought to be unimportant, and that the proteins themselves transmitted genetic traits. The Structure of Chromosomes matter! - We now know that genes are arranged inside chromosomes. - Since entire chromosomes are passed down, multiple genes found in the same chromosomes are passed down together.

Human Disorders caused by Chromosomal Alterations

- Most aneuploidies result in miscarriage. - However, some upset genetic balance less so. - Individuals with certain aneuploid conditions survive, but have a series of traits (a syndrome) associated with the type of aneuploidy.

Development of Female Gametophytes (after pollination)

- As a carpel develops, one or more ovules form deep within the ovary. - Embryo sac: the female gamete that forms inside each ovule. - Megasporangium: tissue where each embryo sac develops. - Megasporangium cells (megasporocyte) undergo meiosis to form 4 haploid megaspores. o 3 of these degenerate, only one survives. o The nucleus of the surviving megaspore divides by mitosis three times without cytokinesis, = one large cell with eight haploid nuclei. o The multinucleate mass is then divided by membranes to form the embryo sac = female gametophytes. - The ovule: consists of the embryo sac, enclosed by the megasporangium (which eventually withers) and two surrounding integuments. - This structure will become a seed if pollinated!

Development of Male Gametophytes in Pollen Grains

- As the stamens are produced, each anther develops four microsporangia, also called pollen sacs. - Within the microsporangia are many diploid cells called microsporocytes. - These undergo meiosis, forming four haploid microspores, each of which eventually gives rise to a haploid male gametophyte. - The microspore then undergoes mitosis once to produce a gametophyte made of 2 cells. Generative cell and the Tube cell.

Sexual, asexual, both

- Asexual reproduction produces offspring without the fusion of egg and sperm - The offspring is a clone, genetically identical to the parent - Asexual reproduction is common in angiosperms and other plants - Many species reproduce asexually through fragmentation, separation of a parent plant into parts that develop into whole plants - In other species, a parent plantʼs root system gives rise to adventitious shoots that become separate shoot systems

The Biological Species Concept (if it gets through chart = different species)

- Biological species concept: a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with members of other such groups Gene flow (interbreeding) between populations holds a species together genetically

Codominance

- Both alleles are expressed not as a gradient or blend but at the same time. Example: Multiple alleles + Codominance - There are many traits which are determined by the presence of multiple alleles or a combination of them. - Traits which have a gradient of phenotypes such as o Blood type o Hair color - The four phenotypes of the ABO blood group in humans are determined by three alleles. o They code for the enzyme that attaches A or B carbohydrates to red blood cells: I^a , I^b, and i. § I^a and I^b are codominant but i is recessive to both o I^a allele adds the A carbohydrate. o I^a allele adds the B carbohydrate o i allele adds neither

Asexual reproduction

- Budding: new individuals arise from outgrowths of existing ones. o In stony corals, buds never separate from parents, forming massive colonies of clonal individuals. o Budding: in hydras, the buds separate into new free-living hydras. - Fission: splitting and separation of a parent organism into two individuals of approximately equal size. o Some corals reproduce via fission. o Common in microorganisms. - Fragmentation and Regeneration: the breaking of the body into several pieces, followed by regrowth of lost body parts. o A single starfish divided into parts will regrow into several new individuals! Parthenogenesis o A form of asexual reproduction. o An egg is formed but develops without fertilization. o Occurs in many bees, ants, wasps, aphids, and others. Haplodiploidy - Unique Haplodiploid sex determination shared with other Hymenoptera. o Fertilized egg: becomes queen or worker, diploid o Unfertilized egg: becomes male, haploid (half of chromosomes) Parthenogenesis - Among vertebrates, parthenogenesis is a rare response to low population density. - Female Komodo dragons for instance, will produce eggs asexually if no males are available. - This provides a population a way to survive an absence of males, but lowers genetic variability.

Down Syndrome (Trisomy 21)

- Caused by an extra copy of Chromosome 21. - Results in: o Mental impairment, Stunted growth, Low muscle tone, Distinctive facial characteristics, Potential heart issues. - One of the most common aneuploidies, affecting approximately 1:850 children. - Risk of Trisomy 21 increases with mother's age. - This correlation has not yet been fully explained o Most likely caused by nondisjunction in meiosis I. o Some research points to age-dependent abnormality in meiosis - meiosis gets harder when the person ages

The Origin of Species

- Charles Darwin was an English naturalist, geologist, and biologist. - He was one of the leading contributors to understanding of evolutionary biology. - A wealthy son of a family of abolitionists in the 1800s. - As a young man, he was a bit of a layabout, loafing around colleges, quitting the medical program at Edinburgh (to his father's horror) and generally finding school to be dull. - Eventually made his way to Christ's College in Cambridge, where he became obsessed with naturalism - Darwin set out on a voyage in a ship called the HMS Beagle, a private research venture to chart the coasts around South America, then circumnavigating the earth. o Along the way, he collected specimens, made observations, and wrote copious notes - In the Galápagos Islands, Darwin observed plants and animals found nowhere else on Earth. o Many resembled animals found elsewhere, but with specialized adaptations for this ecosystem. o For instance, the flightless cormorant or giant tortoise. o Additionally, he made his famous observations of the beaks of finches here. § Each finch species seemed to have a beak well-suited to their lifestyle. § HOW did these adaptations occur?

Different dominance patterns

- Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical. o Normal for peas - In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties. - In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways.

Complete Dominance

- Complete dominance: when phenotypes of the heterozygote and dominant homozygote are identical. - Mendel's peas exhibited complete dominance.

How Meiosis allows for Sexual Reproduction

- Creates gametes for sexual reproduction. - Egg and Sperm cells are both haploid. - When fertilization occurs, a diploid zygote is formed.

Where are the inheritance factors?

- Cytologists observed mitosis and meiosis in 1875 and 1890, respectively. - Chromosomes separate during meiosis. - They become paired again with new homologs after fertilization. But for a long time, scientists had no idea what they did

The Angiosperm life cycle

- Over the course of seed plant evolution, gametophytes reduced in size. - Now wholly dependent on the sporophyte for nutrients - In angiosperms, most reduced of all plants, only a few cells.

Alterations of Chromosome Structure

- Errors in meiosis or damaging agents such as radiation can cause breakage to the chromosome - A damaged gene may realign or become otherwise altered. - Deletion: When a chromosomal segment is removed. - Duplication: A deleted segment attaches to another chromosome, causing a portion of that chromosome to be duplicated. - Inversion: a deleted fragment may reattach to the original, but in the wrong order. - Translocation: a segment of one chromosome moves to a nonhomologous chromosome, and vice-versa. Alterations of Chromosome Structure - Deletions and duplications are especially likely to occur during meiosis. - During crossing over, sometimes chromatids may exchange unequal-sized segments of DNA. o Result: one chromosome with a deletion, one with a duplication. - A diploid embryo that is homozygous for a large deletion is usually missing a number of essential genes. o Typically, this is lethal. - Duplications and translocations are also usually harmful. - Despite not removing genes, it can alter phenotype. Gene expression can be influenced by it's location among neighboring genes, with potentially disastrous effects.

Evolution of Genes with Related Functions: The Human Globin Genes

- Gene family: is a set of several similar genes, formed by duplication of a single original gene, and generally with similar biochemical functions. - The globins are a superfamily of heme-containing globular proteins, involved in binding and/or transporting oxygen. - Humans have several globin genes, divided into two globin families on chromosomes 16 and 11. - They likely arose via duplication, and each gene has accumulated mutations through our evolutionary history. - All current globin genes likely arose from one ancestral globin. - It underwent duplication and divergence into the α globin and β globin genes about 450-500 million years ago

Pleiotropy

- Genes which have more than one phenotypic effect. o Mendel's peas even exhibited it, purples flowers always correlated with colored seed coats - allele for purples flowers affects both traits - For instance, certain heritable diseases have multiple symptoms, but are caused by a single gene. o Cystic fibrosis o Sickle-cell disease - Albinism, mutation in TYR gene o In addition to affecting melanin production, may cause eye issues as well (bc gene codes for more than one thing) - "Frizzle gene" - causes curly feathers in chickens o Also causes birds to have abnormal body temp, higher metabolic rate, higher blood flow rate, greater digestive capacity, and lay fewer eggs

Genetic Recombination and Linkage

- Genetic variation is accumulated in several ways: o Crossing over o Independent assortment of chromosomes o Random fertilization - But what is the chromosomal basis of recombination of alleles? Recombination of Unlinked Genes: Independent Assortment of Chromosomes - Mendel's law of independent assortment. o Unlinked genes recombine in gametes randomly and independently. o 50/50 chance of parentaltype or recombinant offspring. Recombination of Unlinked Genes: Crossing Over - Linked genes can be recombined if the area of the chromosome they're on crosses over. - In heterozygous organisms, the allele for one recessive mutation may cross over with the other homologous chromosome containing the wild type allele. - Diagram from slide??

XXY - Klinefelter (people with XY have an extra X)

- Have testes, but they are abnormally small and the individual is sterile. - Even though the extra X is inactivated, some breast enlargement and other female body characteristics are common. - Affected individuals may have intellectual delays. - About 1 of every 1,000 males is born with an extra Y chromosome (XYY). These males undergo normal sexual development and do not exhibit any well-defined syndrome, but tend to be taller than average

Meiotic Nondisjunction

- If the meiotic spindle doesn't distribute chromosomes correctly, the result is a nondisjunction. - If any of the aberrant gametes (n+/-1) go on to fertilization, the condition is called aneuploidy. - 2n-1 chromosomes (one chromosome doesn't have a homolog) = Monosomic - 2n+1 chromosomes (one chromosome pair has a third copy) = Trisomic - Mitosis will transmit the anomaly to all embryonic cells. o 10-25% of human conceptions experience aneuploidy. o It is the leading cause of early miscarriage.

Sex-linked genes

- In many organisms, biological sex is linked to a specific sex chromosome. - Other sex-linked characteristics often linked to chromosomes. - In reality, sex is more complicated than this, but for our purposes we'll focus on the most basic level. - In mammals and many other animals, the X-Y system typically determines sex, with sperm containing an X or Y. - In some insects, there is no male sex chromosome. This is called the X-O system. - In birds, some fish, and some insects, the Z-W system is used, with eggs containing the sex chromosome. - Social insects like bees, wasps, and ants have no sex chromones at all. They use the haplo-diploid system, with males determined by having haploid cells. Sex-linked genes - Typically, human fetuses begin developing gonads around 8 weeks. - Before that, they are generic and can become ovaries or testes, based on presence or absence of the SRY gene. - If this gene is absent, the embryo will develop into a female phenotype, even if XY (Swyer syndrome).

Sexual/Asexual Reproductive Cycles

- In some organisms, reproductive cycles play a role in whether or not they use asexual or sexual reproduction. - Aphids, as discussed, produce sexually in the fall. - Water fleas (right) reproduce asexually when conditions are favorable, but switch to sexual reproduction in times of stress.

Reproduction Strategies

- K-selection: large body size, long life expectancy, and the production of fewer offspring, usually extensive parental care. o Ex: humans, elephants, gorillas - r-selection: produce many offspring, lower parental care, shorter lifespan. Ex: fruit flies

Linked Genes

- Mendel noted independent assortment, because the genes that code for color and shape were located on different chromosomes. - Linked genes are genes which are almost always passed on together. - This occurs because they are close to each other on the chromosome - Autosomal linked gene: If it is found on one of the first 22 chromosomes - Sex-linked gene: Found on either the X or the Y chromosome - Not only sex specific characteristics are located on these chromosomes - Linked genes conform to Mendel's dependent assortment hypothesis.

Polygenic inheritance

- Mendel studied traits that were "either-or." - There were no half green peas! - But in some traits, such as human skin tone, there are clearly gradients. - These traits are controlled by more than one gene - These are called Quantitative characters. o There is an additive effect of multiple phenotypic characters. o Human skin tone involves at least 3 genes. o The resulting Punnett square is very complex! o More dominant genes = more production

Final Result of Meiosis

- Result: 4 haploid, genetically distinct cells!

Reproductive Cycles

- Most animals reproduce based on a seasonal cycle. o Cycles are regulated by hormones o Those are influenced by day length (photoperiod), temperature, or other environmental cues. o Cycles like this are useful because they conserve resources. o Allowing reproduction only when sufficient resources are available. - Sheep are only fertile in the fall and early winter. o Pregnancy lasts 5 months. o Most lambs born in Spring, when they have highest chance of survival. - Ant colonies produce winged fertile females and males when they reach a certain age. o These alates leave their colonies en masse when environmental conditions are favorable. o Called a nuptial flight, they seek out mates from nearby colonies. o Once mated, queens start new colonies elsewhere o These nuptial flights are timed with weather events to maximize mating success. o If they were not cyclical, resulting sporadic flights would mean much higher rates of mate-finding failure. Dramatic Cycles - This is a periodical cicada, Magicicada septemdicem. - They spend 17 years underground as root-sap feeding nymphs. o Hypothesis: can measure the change in chemistry of the tress to count 17 winters - They emerge in a massive swarm at once to mate, lay eggs, and die over a summer. - Some stray cicadas emerge a year too early or a year too late. o They will likely not find mates at all. o Timing is critical!

Incomplete Dominance (present in animals too - blues hens)

- Neither allele is fully dominant. o When heterozygous, it will show a third phenotype. o A blend of the other two. - Since neither allele is dominant, we use superscript over the allele for color (C). R for red, W for white. - In this snapdragon flower, the F1 generation of true breeding Red (CRCR) and true breeding White (CWCW) is the Pink phenotype (CRCW). - Pink phenotype gametes containing either the CR and CW alleles. - F2 therefore have a 1:2:1 ratio of Red : Pink : White phenotypes. - Discuss with your neighbor: Does this support the blending hypothesis? Why or why not? o No, because in F2 homozygous red and white reappear Incomplete Dominance Summary - Exists in many organisms but follows a similar pattern. - F1 offspring of different phenotype parents will be 100% mixed. o If parents are both homozygous of different colors - F2 offspring will be 1:2:1 of phenotype 1 : mix : phenotype 2.

What Can go Wrong? Meiosis

- Nondisjunction: a chromosome pair doesn't separate during meiosis. As a result, some of the gametes contains extra chromosomes, while others have too few. - Can result in deletion or duplication. Deletion - Deletion: the accidental removal of part of a chromosome. - Can result in survivable but pronounced genetic abnormalities. Duplication - Duplication: cells acquire an extra chromosome due to nondisjunction. - Trisomy = having an extra chromosomes Chromosomes:Too many or too few - Aneuploidy: the condition of having an abnormal number of chromosomes in a haploid set. - Trisomy (having an extra chromosome) is a common aneuploidy. - Down syndrome (trisomy 21) is caused by an extra 21st chromosome. - Others, such as trisomy 13 can cause polydactyly and other defects (above). - Some trisomies are fatal for a fetus.

XXX - Trisomy X

- Occurs once in approximately 1,000 live female births. - Individuals are healthy and have no unusual physical features other than being slightly taller than average. - Higher risk of learning disabilities associated with Trisomy X.

Meiosis II

- Once meiosis I is complete, we're left with 2 cells, each with 1 set of duplicated sister chromatids. - In meiosis II, those cells are separated again, this time, each new cell getting one of the sister chromatids. No genetic information is duplicated! - Prophase II: Spindle apparatus forms. - Metaphase II: Chromatids align at plate, kinetochores attach to microtubules. - Anaphase II: Connecting proteins break down, sister chromatids separate. - Telophase II: Nuclei form and chromosomes decondense. Cytokineses occurs.

Mate Finding

- One obstacle to successful sexual reproduction is finding a suitable mate. For some organisms, this isn't a problem, as mating occurs externally in a large release of gametes (sea sponges). - Sea sponges are simple animals that can reproduce via multiple means. o Budding o Fragmentation o Gemmules: When environmental conditions are poor, they can produce "gemmules" or "survival pods" of unspecialized cells that remain dormant until conditions improve. - BUT sea sponges can also reproduce sexually. o Adults are immobile but release clouds of sperm into the water. o That sperm may drift to another sponge, where it may fertilize their eggs. o Larval sponges emerge from the adult, swim or drift away, then sink to the bottom. o Eventually, a new sessile sponge is formed. Some species seek mates from long distances. This is Creatonotos gangis, the hair pencil moth. - Males secrete a pheromone from dramatic inflatable structures on the end of the abdomen. - Females can smell and follow pheromone plumes for great distances. - Males which had better larval diets grow larger hair pencils. But for some organisms it's more complicated. - Many animals are very choosy about their mates. - This can lead to dramatic sexual selection.

Mapping the Distance Between Genes Using Recombination Data: Scientific Inquiry

- One of Morgan's students, Alfred H. Sturtevant, decided to work out a method for constructing a genetic map, an ordered list of the genetic loci along a particular chromosome. - Hypothesis: the percentage of recombinant offspring, (the recombination frequency) depends on the distance between genes on a chromosome. - If crossing over = random and equally likely to occur at any location on the chromosome... o The greater the distance between two genes, the more points there are between them where crossing over can occur. o So more distance = lower probability of remaining linked o Using recombination data, genes can be mapped onto the chromosome! o This is called a linkage map. Mapping the Distance Between Genes Using Recombination Data: Scientific Inquiry - Sturtevant used b (body color), vg (wing size) and cn (an eye color gene) to build his model. - Distance between genes measured in map units, one map unit = 1% recombination frequency. - Map units are relative distance, not actual measurements. - 9% of the offspring of flies with b and cn are recombinant offspring. - 9 map units apart. A partial linkage map of the Drosophila 2nd chromosome. - Numbers represent relative distance of each gene from the aristae (antennal bristle) gene.

Double Fertilization

- One sperm fertilizes the egg, forming the zygote. - The other sperm combines with the two polar nuclei, forming a triploid (3n) nucleus in the center of the large central cell of the female gametophyte. o This cell will give rise to the endosperm, a food-storing tissue of the seed. - The union of the two sperm cells with different nuclei of the female gametophyte is called double fertilization. - Double fertilization ensures that endosperm develops only in ovules where the egg has been fertilized, thereby preventing angiosperms from squandering nutrients on infertile ovules

Reproductive Cycles and Evolution

- Some reproductive cycles can give us clues about evolutionary history. - For asexual whiptail lizards, all reproduction is performed without males (there are none in this species). o However, egg-laying still follows seasonal "mating season" patterns. o Additionally, some females adopt "male" behaviors, performing mating and courtship rituals that are similar to sexual species of whiptails. o Lizards often swap roles throughout the season. § This is hormonal! o "Female-like" behavior when the level of the hormone estradiol is high. o "Male-like" behavior when the level of the hormone progesterone is high - Paired lizards are more likely to ovulate than solitary ones. - These lizards evolved from a species having two sexes and still require certain sexual stimuli for maximum reproductive success.

Speciation can take place with or without geographic separation

- Speciation can occur in two ways: o Allopatric speciation o Sympatric speciation Allopatric speciation: gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations (and there are selection pressures that force speciation) - For example, the flightless cormorant of the Galápagos likely originated from a flying species on the mainland. - "Barrier" can mean many things! o For example, a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen. o In this example, a mountain isolates two populations of pine trees. - Separated populations may evolve independently through mutation, natural selection, and genetic drift. o Reproductive isolation may arise as a by-product of genetic divergence. - Regions that are isolated or highly subdivided by barriers: more species than areas without! Sympatric Speciation - Populations may experience speciation within the same geographical area. - Habitat isolation or temporal isolation of different members of the same species can cause genetic isolation. - Example: o Remember the apple maggots? o They have two genetically distinct host races § Not quite different species, but close. § They occur sympatrically! § One group uses apples, one uses hawthorn fruit. o Apples and hawthorn are similar fruits, both in the same family. § But they have different phenology. § The flies are also attracted to their natal host. § Ergo; the two fly populations never meet! Sympatric Speciation - In plants, polyploidy is a common cause of sympatric speciation. - A mutant polyploid plant is genetically incompatible with parent species, but may self fertilize. - Its offspring may be able to carry on as a new species. - Sometimes, plant hybrids are polyploid, and form new species that cannot interbreed with parent species.

Reproductive Isolation

- Speciation is often a result of a long-term reproductive isolation. (can't interbred and then grow apart) o Remember, if organisms cannot successfully interbreed, they are considered different species under the biological species concept. - Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring. - Hybrids are the offspring that result from mating between different species. - Isolation can occur before or after mating is attempted.

Totipotency, Vegetative Reproduction, and Tissue Culture

- Test-Tube Cloning: Plants can be cloned by placing cuttings in nutritious media. - This is useful when testing disease resistant crop varieties. - Most houseplants, landscape shrubs and bushes, and orchard trees are asexually reproduced from plant fragments called cuttings. - Grafting: a severed shoot from one plant is permanently joined to the truncated stem of another. - Vegetative Propagation: a shoot cutting is taken. o The wounded end forms a callus, which eventually differentiate into roots Every apple you've ever eaten is a clone! - Apples are grown exclusively on root stocks using grafting. - Since apple seeds do not reproduce true to type, only clones can ensure that a red delicious will always taste like a red delicious. - This means that every apple you've ever eaten is a clone of the first tree of that variety!

Mendel's Laws of Inheritance

- The Law of Segregation: When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. - The Law of Independent Assortment: The alleles of two (or more) different genes get sorted into gametes independently of one another

Limitations of the Biological Species Concept

- The biological species concept cannot be applied to fossils or asexual organisms (including all prokaryotes). - The biological species concept emphasizes absence of gene flow o However, gene flow can occur between morphologically and ecologically distinct species. § For example, grizzly bears and polar bears can mate to produce "grolar bears

Epistasis

- The effect of a gene is dependent on the presence or absence of one or more other genes. o Example: Black lab coats. - In Labrador retrievers (Labs), black (B) coat color is dominant to brown (b). o So, a bb dog will have a brown coat- a chocolate lab. - BUT: there is a second gene that determines if hair gets any pigment at all! - The dominant pigment gene is E. o It results in either black or brown hair, depending on the presence of B or b. o If the lab is homozygous recessive ee, it doesn't matter what configuration of B or b it has, no pigment will be added. o Yellow labs are produced. o But if it even has one dominate E then it will have color depending B combination

Morgan's Flies

- The first solid evidence associating a specific gene with a specific chromosome came early in the 1900s. - Embryologist Thomas Hunt Morgan experimented with flies to study inheritance. - Note: He was skeptical of Mendelian inheritance. - However, he found strong evidence that chromosomes are indeed the location of Mendel's heritable factors. - Sometimes skepticism pays off! Experiments - Morgan chose to use Drosophila melanogaster, the common fruit fly. o There are many benefits to using D. melanogaster. o They reproduces rapidly, one mating pair can produce hundreds of offspring. o They reach maturity in two weeks. - They only have 4 sets of chromosomes, 3 autosome and 1 sex chromosome set. - Female fruit flies have a pair of homologous X chromosomes, and males have one X chromosome and one Y chromosome. - Morgan spent years breeding flies searching for a "mutant," a fly that deviated from the wild type. - After two years of failure, he found a single male with white eyes. A mutant! - Morgan bred his white-eyed male "w" with wild type "w+" females. - All F1 generation were red-eyed, suggesting that the mutation was recessive. - When Morgan bred the F1 flies to each other, he observed the classical 3:1 phenotypic ratio among the offspring. - However, there was something interesting he noticed... o The white eye mutation only appeared in males. o Morgan concluded that somehow the trait was sex-linked, otherwise the trait would be present in females. - Drosophila have X-Y sex determination. o The Y chromosome is smaller and is missing many of the loci of the X chromosome. § It codes for far fewer non-sex related characteristics. - If the mutant recessive allele is on the X chromosome, there will be no homologous chromosome in the males. o Males will pass w to female offspring through X chromosome. - Those female offspring will pass on w in 50% of their eggs. - Since Y chromosomes have no homologous w+ allele, the recessive w allele will always be expressed. - In male, a single mutant allele causes white eyes

Reproductive Structures

- The flower is the sporophytic structure of angiosperms specialized for sexual reproduction. o Comprised of Petals, Sepals, Stamen, and Carpels. o While many plants display indeterminate growth, flowers are determinate. § They stop growing after flowers and fruit are formed. - Carpels and stamens are sporophylls—modified leaves specialized for reproduction. Petals and sepals are sterile modified leaves. o The Carpel contains a stigma, style (stalk), and ovary. o Stigma: a sticky structure that captures pollen. o Ovary: Where the eggcontaining ovules develop. o If fertilized, the ovules become seeds. o Sometimes a single carpel is called a pistil. - The Stamen (microsporophyll) consists of a stalk called the filament and a terminal structure called the anther. o Anther: chambers called microsporangia (pollen sacs) that produce pollen. - Petals are usually brightly colored and used to advertise a fertile flower to pollinators. - Sepals enclose and protect flower buds, and resemble normal leaves. - A Complete flower contains all four organs, incomplete flowers are missing one or more.

The Law of Segregation

- Two alleles for each trait segregate, or separate, during the formation of gametes. - Alternative alleles account for variation in heritable characteristics. - Organisms inherit two alleles. o One from each parent. o Gametes pass only a single allele. o Alleles are segregated during gamete formation. Meiosis Flashback - Remember, by the end of meiosis, each cell has only one version of each allele. - The second is introduced at fertilization. - The allele each gamete gets is decided by chance! Testcrossing - What if we don't know the genotype? - A dominant phenotype (purple) may be homozygous or heterozygous o Homozygous: Two of the same allele. (PP or pp) o Heterozygous: Two different alleles. (Pp) - Test them and see offspring Punnett square - Shows possible combination of alleles in offspring, which each having an equally probable product of fertilization - Used to determine the probability of different allele combinations o The alleles of each parent are written on a side of a box o Alleles are carried across the box o Each box represents a specific percentage o Each box is 25% in this example Probability governs Mendelian inheritance - When a heterozygote (Rr) forms a gamete, the presence of an R or an r is essentially a coinflip. - Probability can be calculated by multiplying the individual probabilities of a sperm or egg having a particular allele. Law of Segregation Review - When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. - Punnett squares can be used to predict genotype combinations. - Homozygous or Heterozygous dominant genotypes express as a dominant phenotype, homozygous recessive genotypes express as a recessive phenotype

Aneuploidy of Sex Chromosomes

- Usually these upset genetic balance less than autosomal conditions. - Likely due to Y chromosome having few genes, or X chromosomes being half inactive. - X-based aneuploidies may be mosaics in XX individuals.

Deletion - William's Syndrome

- Williams syndrome (Deletion of a region of chromosome 7- about 27 genes) o Facial changes, High empathy, Over friendliness, Highly verbal skills relative to IQ, Heart problems

X Inactivation specifics

- X Inactivation involves modification of the DNA and histones, including attachment of methyl groups (-CH3) to DNA nucleotides. - A particular region of each X chromosome contains several genes involved in the inactivation process. - The gene XIST (for X-inactive specific transcript), becomes active only on the chromosome that will become the Barr body. - Multiple copies of the RNA product of this gene attach to the X chromosome on which they are made, eventually almost covering it. - This RNA process initiates X inactivation.

Alterations to chromosome number or structure

Alterations to chromosome number or structure - The phenotype of an organism can be affected by small-scale changes involving individual genes. - Random mutations = new alleles, which can lead to new phenotypic traits. - Large-scale chromosomal changes can also affect an organism's phenotype. How do Chromosomes get Damaged? - Physical and chemical disturbances. - Errors during meiosis - Large-scale chromosomal alterations in humans and other mammals often lead to miscarriage. - These commonly cause various developmental disorders. - Plants appear to tolerate such genetic defects better than animals do.

Day 1 Summary

Summary - Meiosis creates 4 unique haploid cells out of one diploid cell. - It is essential for sexual reproduction. - It is a major source of genetic variability.

Mendel Experiments

But- - Mendel had no idea what genes were! Let alone alleles or chromosomes. He called them "inheritance factors" or "elements." - Mendel's Question: If blending were correct, all traits of a species to eventually converge, which doesn't happen. - Additionally, how could traits skip a generation if blending was true? So, he Experimented - True breeding flowers: A plant that when self-pollinated, only produce flowers with the same traits as the parent over multiple generations - Mendel crossed true breeding plants (homozygotes) with each other. - Mendel could easily control which plants mated with others by artificial pollination. - P= Parental Generation Results - When pollen from a white flower was transferred to a purple flower, the first filial generation (f1) all had purple flowers. The result was the same for the reciprocal cross, which involved the transfer of pollen from purple flowers to white flowers - So, blending was out. o If the blending model of inheritance were correct, the hybrids from a cross between purple-flowered and white-flowered pea plants would have pale purple flowers, a trait intermediate between those of the P generation. o Instead, all the F1 flowers had purple flowers! - Mendel called this trait "dominant." - What Mendel discovered was that the presence of a dominant allele caused that phenotype to express, even when the organism is a heterozygote! - Further question; where did the white color go? Well, it wasn't gone! - If allowed to self-pollinate or cross-pollinate, white flowers reappeared in the F2 generation. - 705 of the plants had purple flowers, and 224 had white flowers. These data fit a ratio of approximately three purple to one white.

Climate Change and Reproductive Cycle

Climate Change - Since many reproductive cycles are tied to climate, warming can negatively impact mating. Greenland Caribou - Caribou migrate to calving grounds in the spring to give birth. - This coincided with time when plants were most nutritious. - Caribou migration is triggered by day length (photoperiod), not temperature. - Since ~2006, Spring temperatures have risen and plants bloomed early. - Result: Caribou arrive too late to take advantage of spring bloom. - 75% reduction in caribou births in 30 years.

Mendel: recessive

Conclusion: - The "heritable factor" for the recessive trait (white flowers) had not been destroyed, deleted, or blended. - It was masked by the presence of purple flowers, which was the dominant trait. - Mendel observed similar patterns in other traits, such as seed color, seed shape, pod color, pod shape, flower position, and stem length. - All exhibited dominant and recessive traits, all had similar ratios in F2. - Mendel bred peas in different combinations over generations for 8 years.

Disorders Caused by Structurally Altered Chromosomes

Disorders Caused by Structurally Altered Chromosomes - Many deletions can cause severe problems. - Even a deletion of just part of chromosome 5 causes cri du chat ("cry of the cat") syndrome. - Individuals with cri du chat typically have smaller than typical heads, severe learning disabilities, and a cat- like cry. - Most do not survive past childhood. Structurally Altered Chromosomes - Translocations can occur during mitosis, some are implicated in certain cancers. - Chronic myelogenous leukemia (CML) occurs when a large portion of C22 exchanges with a small fragment tip of C9. - Called the "Philadelphia chromosome." - Creates a new "fused" gene that causes uncontrolled cell cycle progression (cancer).

seed dispersal

Dispersal - Wind - Many seeds (or rather, their very small fruits) have evolved to disperse by wind. - Many of these have even developed gliding methods! Dispersal - Water - Coconuts are buoyant and are capable of floating until they reach a suitable germination spot. Dispersal - Animals - Animals are common carriers of seeds. - Some dry fruits are adapted to stick to animal's bodies. - Some are designed to pass through an animal's gut. Some others trick animals into dispersal Elaiosomes - Some seeds have developed an edible "cap" called an Elaiosome. - This cap is highly nutritious for ants. - Ants will carry the seeds back to their nests, eat the elaiosome, and leave the seed intact. - They carry the seed to their waste piles, which are rich in nutrients. Seed dormancy - Seeds don't immediately start growing. - They require particular conditions to break dormancy. - Many require moisture, some require dramatic forces like fire!

Does Dominant = Common? - Not necessarily

Does Dominant = Common? - Not necessarily Limitations on Dominant Traits- Progeria - Some inherited disorders are caused by dominant alleles. - Yet, they stay very rare in the general population. o Example: Progeria is a disorder caused by a dominant allele. o Leon Botha was the oldest living person with Progeria, passing away at 26 (average age of death: 14). - Progeria is caused by a mutation in the LMNA gene. - Without it, nuclear envelopes are damaged. - This mutation is dominant. The allele causing Achondroplasia dwarfism is also dominant. - A heterozygous parent with dwarfism and a typical height parent have a 50% of dwarfism in their children. So what gives? - Progeria affects about 1 in 20 million people around the world. - Achondroplasia dwarfism affects about 1 in 15,000 to 1 in 40,000 people. - So if the alleles for dwarfism and progeria (among others) are dominant, why are people with dwarfism or progeria so uncommon? A disorder can be dominant but remain rare if: - It can be passed on but is simply uncommon in the population - Dwarfism. - Causes reproductive issues or sterility - Progeria - Is life-threatening - Tay Sachs

Environmental impact on phenotype

Environmental Factors - Some phenotypes for a character depend on the environment as well as genotype. - In humans, nutrition affects height, though that has a genetic component as well. - Exposure to sun affects melanin production. - IQ scores improve with test-taking experience. Environmental impact on phenotype - Different environments can change the expression of the same gene. - Hydrangea flower color dependence on the soil acidity. o Basic soil: redish o Acidic: bluish, purplish

Evolution of Genes with Novel Functions

Evolution of Genes with Novel Functions - In our globin example, all the different genes in the family perform similar functions (carry oxygen). - An alternative scenario is that one copy of a duplicated gene can undergo alterations that lead to a completely new function for the protein product. Example: The genes for lysozyme and α -lactalbumin. - Lysozyme is an enzyme that helps protect animals against bacterial infection by hydrolyzing bacterial cell walls. - α -lactalbumin is a nonenzymatic protein that plays a role in milk production in mammals. - α -lactalbumin and lysozyme have very similar structure. - Genes to produce both proteins are found in mammals, but only lysozyme is found in birds. - At some time after the lineages leading to mammals and birds had separated, the lysozyme gene was duplicated in the mammalian lineage but not in the avian lineage. o One copy of the duplicated lysozyme gene evolved into the gene that encodes for α - lactalbumin. This formed a completely new function in the mammal clade: milk production

Gregor Mendel

Gregor Mendel - Augustinian friar who became a monk because it allowed for an education he didn't have to pay for. - Was a substitute high school teacher, but failed his oral exams to become a full teacher in 1850. - In 1851, he was sent to the University of Vienna to study to study the natural sciences - Upon returning to the monastery, he began a series of scientific experiments on mice, bees, and pea plants. - Used pea plants as his model organism to learn about heredity - Mendel's experiments on the hereditability of traits in pea plants established many of the rules of heredity, now referred to as the laws of Mendelian inheritance. Before Mendel - People have been grappling with how heredity works for thousands of years. - Pangenesis: the theory that each unit or cell of the body throws off tiny particles (pangenes) which are collected in the reproductive cells as the units of hereditary transmission. o Darwin even believed in a variation of this! - Preformation: the idea that a new organism was fully formed but tiny before implantation (either in the egg or the sperm). - Blending: the belief that parents traits simply blended into an intermediate form. • Blending was commonly accepted during Mendel's time.

Haploid/Diploid, Homologous chromsomes, alleles

Haploid / Diploid - Haploid: Cells having a single set of unpaired chromosomes (n). - Diploid: Cells containing two complete sets of chromosomes, one from each parent (2n). Homologous Chromosomes - A pair of chromosomes. - They have the same size and shape. - Same organization (equivalent loci- singular locus). - They have the same genes, but may have a different version of that gene! o Have different alleles Alleles - Allele - different version of a gene. o An allele is the form that the gene can take, or how well it can do the job. - Example: This highlighted gene codes for eye color. Each homologous chromosome has the same gene, but one codes for blue (b) and the other codes for brown (B). B and b are alleles.

How DNA reconfiguration contribute to evolution.

How DNA reconfiguration contribute to evolution. - Now that we have explored the makeup of the human genome, let's see what its composition reveals about how the genome evolved. Duplication of Entire Chromosome Sets - Most polyploidies are lethal. - But in rare cases they can facilitate the evolution of genes. - In a polyploid organism, one set of genes can provide essential functions for the organism. - The genes in the extra sets can accumulate mutations, which may persist in offspring. - In this way, genes with novel functions can survive! - The outcome of this accumulation of mutations may eventually be the formation of a new species. - Rare in animals, but relatively common in plants. Alterations of Chromosome Structure - We've recently experienced an explosion in genomic sequence information. - It's now possible to compare the chromosomal organization of different species in detail. Humans and apes - At some point in our evolutionary history, humans lost their 24th chromosome. o It combined with our 23rd. o Other apes have 24 chromosomes, so this seems to be unique to Homo sapiens. o 12th and 13th chromosome of chimp fused into 2nd chromosomes Mouse and Humans - In this example, DNA sequences similar to our Chromosome 16 are spread our through 4 mouse chromosomes. - But the sequences themselves are very similar across clades! - This finding suggests that the DNA sequence in each block has stayed together in the mouse and human lineages since the time they diverged from a common ancestor. - Humans have simply combined them into a single chromosome. Duplication and Divergence of Gene- Sized Regions of DNA - Unequal crossing over during prophase 1 can result in duplication on one chromosome, and deletion on another. - This duplication is found in multigene families, such as the globin family.

How Transposable Elements Contribute to Genome Evolution

How Transposable Elements Contribute to Genome Evolution - Transposable elements have persisted as a large fraction of some eukaryotic genomes. - They seem to play an important role in shaping a genome over evolutionary time. - They promote recombination, disrupt cellular genes, or carry entire genes or exons to new locations. How Transposable Elements Contribute to Genome Evolution - Eukaryotic transposable elements are of two types o Transposons, which move by means of a DNA intermediate and require a transposase enzyme o Retrotransposons, which move by means of an RNA intermediate using a reverse transcriptase - Transposable elements may carry a gene or groups of genes to a new position. - If the transposable element inserts within a regulatory sequence, the result may be increased or decreased production of one or more proteins. - Transposable elements may also create new sites for alternative splicing in an RNA transcript - Like we discussed earlier, most of these recombinations are probably detrimental. - BUT: over the course of evolutionary time, an occasional recombination event of this sort may be advantageous to the organism.

How does Linkage Affect Inheritance?

How does Linkage Affect Inheritance? - Morgan performed other experiments on Drosophila, to determine how linked traits affect inheritance. - The tested characters were body color and wing shape. - Wild-type flies have gray bodies and normal-sized wings. - Morgan bread them with doubly mutant flies with black bodies and wings much small, vestigial wings. The Experiment: - Morgan wanted to know whether the genes for body color and wing size are genetically linked and, if so, how this affects their inheritance. - The alleles for body color are (gray) and b (black), and those for wing size are (normal) and vg (vestigial). - Question: Will the offspring exhibit black body and vestigial wings together? Or will the mutations separate? - Predictions: o 1 : 1 : 1 : 1 - Predicted ratio for genes on different chromosomes. o 1 : 1 : 0 : 0 - Predicted ratio for genes on same chromosomes. - Results: Most flies were of a parental phenotype o Either completely wildtype or mutant - However, a small number were of a recombinant phenotype. o Recombinant: an offspring whose phenotype differs from the true breeding P generation parents. § Some flies with grey body vestigial wings, or black body normal wings o If the genes are linked, how could this be?

Meiosis

Meiosis - Another form of cell division. - In meiosis, one diploid cell becomes four genetically unique haploid cells. - Gametes (sex cells) are produced via meiosis How does this work? - Interphase: Chromosomes duplicate, forming 2 identical sister chromatids. - Meiosis I: Homologous chromosomes "cross over" some genetic information, then separate. - Prophase I - Metaphase I - Anaphase I - Telophase I &Cytokinesis - Meiosis II: Sister chromatids separate. - Prophase II - Metaphase II - Anaphase II - Telophase II &Cytokinesis

Inheritance may be more complex than simple punnett squares

Inheritance = may be more complex than this - Peas have relatively simple phenotypic expression. - Almost all of their traits are determined by a single allele. - One is completely dominant, one is completely recessive. - This makes them a great model organism, but not all organisms are this simple! When things get complicated - Inheritance of characters by a single gene may deviate from simple Mendelian patterns when: o When alleles are not completely dominant or recessive o When a gene has more than two alleles o When a gene produces multiple phenotypes

Inheritance of X- Linked Genes

Inheritance of X- Linked Genes - Males and females inherit different numbers of X chromosomes. - There are very few Y-linked genes, many help determine sex. - X chromosomes have genes for many characters unrelated to sex. - XY parents pass may pass X or Y to their offspring. - XX parents can only pass X-linked alleles to all offspring. In this example, if the XY parent is color-blind, that mutant allele is linked to the X chromosome. - This is why most people who are color-blind are XY. - It's recessive, so if you have XX, you'd need 2 colorblind alleles to have that phenotype. - However, if you only have one X Chromosome, "homo/heterozygous" loses its meaning. If you have the allele, you have the phenotype. o This is called "hemizygous," Greek for "half." - Some X-linked disorders are much more serious than color blindness. - Duchenne muscular dystrophy, which affects about one out of 3,500 males born in the United States, results in progressive weakening of muscle tissue. - Hemophilia is an X-linked recessive disorder that prevents the formation of blood-clotting proteins.

Mendel's Experimental, Quantitative Approach + Terms

Mendel's Experimental, Quantitative Approach - Mendel suspected blending was incorrect, as he noticed traits skipping generations in his garden flowers. - Around 1857, he began breeding peas in the abbey garden to study how they inherited traits. - Peas are a good model organism because they have a large degree of variation within a single species. - Some have purple flowers, others have white flowers, for instance. A Few Terms - Character A feature with variable structure o Must be inheritable o E.g.: Flower color - Trait o Individual variations on a character o E.g.: purple or white flowers Flashback- Alleles - Alleles are genetic variations of a trait o Symbolized by letters. o Homozygous: Two of the same allele. o Heterozygous: Two different alleles. - Genotype o Genetic makeup. - Phenotype o "Physical" expression of your alleles (genes). o E.g. seed color, seed shape, chemical production. In human terms, our visible eye color is a phenotype

Meiosis I: Metaphase I, Anaphase I, Telophase I

Metaphase I - In Meiosis, homologous chromosomes line up together at the metaphase plate, in mitosis, individual chromosomes line up. o Independent assortment - Microtubules attach to kinetochores located at the centromeres. Independent Assortment of Chromosomes - At metaphase I, the homologous pairs, each consisting of one maternal and one paternal chromosome, are situated at the metaphase plate. - Each pair may orient with either its maternal or paternal homolog closer to a given pole—its orientation is as random as the flip of a coin. - Thus; each daughter cell gets a random mix of maternal and paternal chromosomes. - This massively increases genetic diversity. Anaphase I and Telophase I - In Meiosis, anaphase/telophase I ends with separated homologs, but sister chromatids attached by the centromere. In mitosis, sister chromatids separate during anaphase.

Mitosis Review/Vocab

Mitosis Review: - New cells are genetically identical to parent cells, same number of chromosomes - Used for repair, growth, or asexual reproduction Asexual reproduction - Reproduction driven by mitosis - Offspring are genetically identical to parents - Hydras, pandos Sexual reproduction - The combination of 2 sex cells (gametes/spores) to create a zygote (offspring). - Genetic information from two individuals are combined. - Result: genetic diversity among offspring. First, some vocabulary - Haploid / Diploid (Ploidy): The number of chromosome sets in a cell. - Homologous Chromosomes: Two chromosomes in a pair - normally one inherited from the mother and one from the father. - Alleles: one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Other Definitions of Species

Other Definitions of Species - Other species concepts emphasize the unity within a species rather than the separateness of different species The morphological species concept defines a species by structural features. o It applies to sexual and asexual species but relies on subjective criteria o But this has its limitations... subjective § Many species look the same but aren't, others look different but are the same The ecological species concept defines a species in terms of its ecological niche - It applies to sexual and asexual species and emphasizes the role of disruptive selection. - Many species definitions have been proposed; the usefulness of each depends on the situation and the research questions being asked

Pedigree

Pedigree - While new advanced tools exist to study human genetics, Mendelian models still play an important role. - One such role is the use of family pedigrees. - Using pedigree analysis, we can construct the history of a trait in human lineage, and predict its future. In this example, the "Widow's Peak" trait is traced through these sister's family tree - Note that their parents both have the widow's peak trait, but only one sister does. - Ergo: their parents must be heterozygotes, and that the allele must be dominant. In this example, the inability to taste a chemical called PTC is tracked. - Notice the first born 3rd generation daughter has the trait (cannot taste it). - Since she has this trait, it must be recessive, otherwise her parents would both have it as well. Pedigree - Pedigrees can be used for the novelty of predicting mundane traits. - But they are a more serious matter when the alleles in question cause disabling or deadly diseases. - For these, the same techniques of pedigree analysis apply.

Pollination

Pollination - Plants which sexually reproduce require pollen to fertilize an ovule. - Since plants don't move (very much), they require an outside force to move their pollen to the intended target. Pollination by wind - Grasses and many trees pollinate by wind. - They release massive quantities of smaller-size pollen. - This makes up for the randomness of using wind, but is a nightmare for anyone with allergies! Pollination by bees - Approximately 65% of flowering plants require insects for pollination. - Even higher percentage of human crops. - Bees are the most important insect pollinators. - Bees and flowers have coevolved closely. o Bees can see the UV spectrum, so some flowers have evolved "bullseyes" that bees can see clearly. o Flowers that use bees have sweet odors to attract foragers to nectar. Pollination by moths and butterflies - Usually sweet-smelling flowers. - Butterflies attracted to many bright colors - Moth-pollinated flowers are typically white or yellow, to help stand out at night. Pollination by flies - Some flowers use flies to pollinate. - Most use flowers as a nectar source, and transmit pollen similarly to bees. - Some flowers mimic the smell of decay to lure in fly pollinators. - Pawpaw flowers (right) smell like vinegar when in bloom! Pollination by bats - Much like moths, these flowers are usually white or yellow. - Some desert bats feed on nectar, and collect pollen on their fur Pollination by birds - Some flowers are pollinated by birds, particularly hummingbirds.

Pollination: Co-evolution

Pollination: Co-evolution - Some plants have evolved partnerships with very specific pollinators. - When Darwin saw this flower, he inferred there was somewhere a moth with a proboscis evolved to pollinate it. o He was right! - Coevolution: The joint evolution of two interacting species, each in response to selection imposed by the other. o Many plants have coevolved with a single species that can pollinate them Coevolution to the extreme- the fig wasp - Figs have inverted flowers. - Pollen-laden female wasps enter an unripe fig through an opening called an ostiole. - Once inside, she lays eggs inside some flowers, pollinating as she moves. - Newly hatched wasps mate, then the males dig tunnels out of the fruit for the females. - Males die inside the fruit. - Most fig species have evolved to be pollinated by a single wasp. Plants that Trick Pollinators - This is a parasitic corpse flower, Rafflesia arnoldii. - It looks and smells like rotting meat. - It uses flies to pollinate, tricking them into laying eggs on its massive petals. - Flies pick up pollen, but their eggs are doomed. Plants that Trick Pollinators - This is a bee orchid, Ophrys apifera. - Its petals mimic the appearance of a female bee, and it produces similar pheromones. - Male bees will attempt to mate with the flower, and in the process pollinate. - But they get nothing out of this!

Postzygotic barriers

Postzygotic barriers: Mating occurs, but proper reproduction is blocked by reduced hybrid viability, hybrid sterility, or hybrid breakdown. Reduced hybrid fertility Reduced hybrid viability: Genes of the different parent species may interact and impair the hybridʼs development or survival in its environment. - Even if hybrids are healthy, they may be sterile. Hybrid breakdown: Some firstgeneration hybrids are fertile, but when they mate with each other or with either parent species, offspring of the next generation are feeble or sterile

Prezygotic barriers:

Prezygotic barriers: Mating is prevented by geography, time, behavior, anatomy or some other factor. o No mating is attempted or completed! o Block fertilization from occurring by § Impeding different species from attempting to mate § Preventing the successful completion of mating § Hindering fertilization if mating is successful Habitat Isolation - Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers o Example: The apple maggot and blueberry maggot fly. o They are very similar organisms, but use different hosts for their larvae, so never interact. Temporal Isolation - Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes. o In North America, western spotted skunk and eastern spotted skunk's ranges overlap. o But their reproductive cycles occur at different points in the year, so do not interbreed. Behavioral Isolation - Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers to mating. - Many birds require a species-specific ritual to identify a potential mate. - Some animals use songs to segregate between conspecifics. - Many insects use auditory cues, and are only interested in cues of their own species. Mechanical isolation: Morphological differences can prevent successful completion of mating - In these different snail species, their shells whirl in the opposite direction. - This prevents them properly aligning and mating. Gametic Isolation: Sperm of one species may not be compatible with eggs of another species. - This is common when species may reproduce with massive spawning events. - The drifting sperm of a sea urchin isn't seeking out conspecifics. - It is simply incompatible with the eggs of other urchin species.

Meiosis I Prophase and Crossing over

Prophase I - In both, chromosomes duplicate during Interphase. - In Meiosis, homologous chromosomes pair up and crossing over occurs. o Important source of genetic variation in offspring Crossing Over - After interphase, the chromosomes have been duplicated and the sister chromatids are held together by proteins called cohesins. - Early in prophase I, the two members of a homologous pair associate loosely along their length. Each gene on one homolog is aligned precisely with the corresponding allele of that gene on the other homolog. - The DNA of two nonsister chromatids—one maternal and one paternal—is broken by specific protein complex at precisely matching points - Next, the formation of a zipper-like structure called the synaptonemal complex holds one homolog tightly to the other. The chromatin continues to condense. - During this association, called synapsis, the DNA breaks are closed up so that each broken end is joined to the corresponding segment of the nonsister chromatid. - Thus, a paternal chromatid is joined to a piece of maternal chromatid beyond the crossover point, and vice versa. - These points of crossing over become visible as chiasmata (singular, chiasma) after the synaptonemal complex disassembles and the homologs move slightly apart from each other. - Homologs remain attached via cohesion. - They move together to the metaphase plate. - In both, chromosomes duplicate during Interphase. - In Meiosis, homologous chromosomes pair up and crossing over occurs. o Important source of genetic variation in offspring Crossing Over - After interphase, the chromosomes have been duplicated and the sister chromatids are held together by proteins called cohesins. - Early in prophase I, the two members of a homologous pair associate loosely along their length. Each gene on one homolog is aligned precisely with the corresponding allele of that gene on the other homolog. - The DNA of two nonsister chromatids—one maternal and one paternal—is broken by specific protein complex at precisely matching points - Next, the formation of a zipper-like structure called the synaptonemal complex holds one homolog tightly to the other. The chromatin continues to condense. - During this association, called synapsis, the DNA breaks are closed up so that each broken end is joined to the corresponding segment of the nonsister chromatid. - Thus, a paternal chromatid is joined to a piece of maternal chromatid beyond the crossover point, and vice versa. - These points of crossing over become visible as chiasmata (singular, chiasma) after the synaptonemal complex disassembles and the homologs move slightly apart from each other. - Homologs remain attached via cohesion. - They move together to the metaphase plate.

Rearrangements of Parts of Genes: Exon Duplication and Exon Shuffling

Rearrangements of Parts of Genes: Exon Duplication and Exon Shuffling - Rearranging DNA sequences within genes has also contributed to genome evolution. - Exons: The sequence of DNA present in mature messenger RNA, some of which encodes the amino acids of a protein. - Introns may have promoted the evolution of new proteins by facilitating the duplication or shuffling of exons. Rearrangements of Parts of Genes: Exon Duplication - An exon often codes for a protein domain, a distinct structural and functional region of a protein molecule. - Unequal crossing over may lead to duplication of a gene on one chromosome and its loss from the homologous chromosom - Similarly; a particular exon within a gene could be duplicated on one chromosome and deleted from the other. - The gene with the duplicated exon would code for a protein containing a second copy of the encoded domain. - This change in the protein's structure might: o Increase its stability o Enhancing its ability to bind a particular ligand o Alter some other property! - Many protein-coding genes have multiple copies of related exons, which presumably arose by duplication and then diverged. - Collagen has multiple copies of similar exons, which produce a long and repetitive amino acid sequence. Exon Shuffling - Exon Shuffling: The occasional mixing and matching of different exons either within a gene or between two different (nonallelic) genes. - Caused by errors in meiotic recombination. - Example: the gene for tissue plasminogen activator (TPA). - Arisen by several instances of exon shuffling and subsequent duplication. - The TPA protein is an extracellular protein that helps control blood clotting.

Recessive Disorders

Recessive Disorders - Most recessive disorders are passed on by heterozygous parents displaying the typical phenotype. o i.e.: if Aa and Aa have a baby, there is a ¼ chance of an aa genotype- causing albinism. - While it's rare for two carriers to accidentally have children, this becomes much more common with inbreeding. o Because close relatives are more likely to share recessive traits with each other. o The Habsburg dynasty was a famous example of long-term royal inbreeding. § Due to ~200 years of consanguineous (close relative) marriages, many otherwise rare disorders accumulated in this family. § Culminating in Charles II "The Bewitched", who had at least two rare recessive disorders: · Pituitary hormone deficiency (which can result in infertility) and distal renal tubular acidosis, a cause of kidney failure. But Does Recessive = Rare? - Not necessarily! o Simply because a trait is frequent in the population doesn't mean the trait is dominant Sickle Cell trait is recessive, but common - The mutation for sickle cell trait may have been selected for! - The trait confers a degree of resistance to malaria. - You would expect this trait to persist in areas with high malaria pressure. Sickle Cell - Heterozygote advantage - A person who is heterozygous for this trait is referred to as a carrier. - They are conferred an advantageous resistance to malaria. o Sickle cells have porous membranes that leak nutrients which the single-celled parasites need to survive, killing the parasites more quickly. - However, homozygous recessive results in sickle cell disease.

Speciation

Speciation, the process by which one species splits into two or more species, is at the focal point of evolutionary theory - Microevolution consists of changes in allele frequency in a population over time o Example: The Peppered Moth Biston betularia § A relatively common moth in the UK. § This moth has two distinct color morphs, a light and dark. · During the industrial revolution, soot covered buildings and trees, so the dark morph became more prevalent (top). · After pollution decreased, selection pressure reversed, and the light moth became the most common type again (bottom). · This is a change in allele frequency, microevolution. - Macroevolution refers to broad patterns of evolutionary change above the species level - Speciation forms a conceptual bridge between microevolution and macroevolution

Sexual Reproduction is an Enigma

Sexual Reproduction is an Enigma - Sexual reproduction is common but honestly a mystery. - The disadvantages in this method are obvious: o Fewer offspring can be produced - Despite this, sexual reproduction seems to have a few upsides. o In times of stress (environmental upheaval, pathogen breakouts, etc) genetic variability may ensure some survival. o Clonal offspring are more vulnerable to crises. - In times of stability, asexual reproduction produces more offspring and thus is generally considered preferable. Example: Insecticide Resistance - Resistance to poison is a trait selected for in many insects. - Through random mutations, some insecticides become far less effective against some pests. - The insects with that mutation survive to reproduce more, thus selecting the resistant alleles. - Result: large populations of insects resistant to poisons! Example: DDT - In addition to environmental concerns, DDT is functionally useless in many parts of the world due to widespread mosquito resistance.

Sexual Selection

Sexual Selection - Sexual selection is a mode of natural selection. - Rather than choose for survival adaptations, mates choose certain traits, which are then passed down. o These traits may be fitness proxies. o This can lead to very exaggerated traits in one sex! Birds of Paradise - In the birds of paradise, the males have adapted large showy displays and courtship behaviors. o What could be the purpose of these? - One hypothesis: It's a proxy for fitness. - It shows endurance to perform the rituals. Sometimes the displays are truly unwieldy. This is a male fiddler crab. - They have one normal sized claw, one huge one. o They "wave" them in a mating ritual to attract female attention. o This giant claw takes energy to wave around. o But they're useless when it comes to feeding. o Yet, females tend to prefer larger claws. o There may be a material reason for this! - Male fiddler crabs dig burrows that females eventually lay eggs in. o Those eggs need certain degrees of air flow for maximum fitness. o Larger claws tend to correlate with larger burrows. o This is a fitness proxy!

Sexual vs Asexual Reproduction

Sexual vs Asexual Reproduction - What does sexual reproduction have to offer organisms evolutionarily? - What are the pros and cons? Sexual reproduction advantages: Genetic Variation - Mating/fertilization o A massive number of possible combinations can arise from fertilization! - Meiosis itself o Independent assortment o Crossing over o Meiotic errors and mutations Genetic Variation - The resulting possible genetic variability of the zygote is incredibly high. - In humans, each male and female gamete represents one of about 8.4 million (223) possible chromosome combinations. - Each Zygote = 70 trillion diploid combinations possible! - Leads to greater adaptability of sexual reproducing organisms Evolutionary Benefits - Genetic diversity is a driver of evolution. - Darwin: a population evolves through the differential reproductive success of its variant members. - Individuals best suited to the local environment leave the most offspring. - Thus, natural selection results in the accumulation of genetic variations favored by the environment. Sexual Reproduction- Disadvantages - In a stable environment, asexual reproduction may be preferable. - Sexual reproduction is more energetically expensive. - Mate-finding is not guaranteed. The Best of Both Worlds? - Aphids have a complex reproductive life history. - Females have asexual and sexual generations, which arise at different points in a single season. - Advantage: Early, rapid asexual reproduction, later reproduction has increased genetic diversity.

The XX Conundrum

The XX Conundrum - Female mammals tend to have XX, twice the number inherited by males. - Question: do females make twice the amount of proteins encoded by X-linked genes as males? • - Answer: No! - One X chromosome in each cell in female mammals becomes inactivated during early embryonic development. - The inactive X condenses into a compact object called a Barr body which lies inside the nuclear envelope. - Most of the genes in the Barr body do not express. o One exception: In the ovaries, Barr body chromosomes are reactivated, resulting in every female gamete (egg) having an active X after meiosis. - British geneticist Mary Lyon found that the X chromosome that will form the Barr body is usually randomly selected. - Ergo: XX mammals consist of a mosaic of two types of cells: those with the active X derived from the father OR those with the active X derived from the mother! X Inactivation Mosaicism - This mosaicism manifests in several ways. - In cats : tortoiseshell or calico colorations. - In humans: recessive X-linked mutation that prevents the development of sweat glands. Some areas can sweat, others can't!

The Law of Independent Assortment

The alleles of two (or more) different genes get sorted into gametes independently of one another The Law of Independent Assortment - In earlier tests, Mendel followed a single character, such as flower color. - But many characters can have more than one trait! - Seeds can be different colors AND different textures. Question: Are the alleles that were inherited from each parent linked? (Are they dependent?) The law of independent assortment was worked out by following these two traits: color and wrinkles - If the alleles that are often observed together are dependent (ie: YR or yr are passed down together), you would expect a 3:1 Phenotypic ratio. - If the alleles are independent, you'd expect a much more complex Punnett square, since each allele has an equal chance (1/4) of being passed down. - Result: Each parent is equally likely to transmit Y, y, R, or r, in any combination - Mendel discovered inheritance for traits are not tied to one another simply because they appear together. The Law of Independent Assortment - Alleles/gene separate independently during gamete formation resulting in 4 new phenotypes! - This ratio was always approx 9:3:3:1.

So what is a species?

Theories: Morphological diversity (but issues) Similarity and Diversity - Not all species are defined by morphological differences. - Many species display massive morphological diversity, while some different species are morphologically identical.

Unique Ploidies

Unique Ploidies - Some organisms have more than two complete chromosome sets in all somatic cells. - The general term is "Polyploidy" - Triploidy = 3n, Tetraploidy = 4n, etc. - Can arise by accident, but some organisms are naturally polyploids. o Much more common in plants. o A polyploid organism is more likely to appear typical than an aneuploid. Plant polyploidies - Polyploidy is found in ~30% of cultivated crops. - Octoploid strawberries grow to massive size to accommodate all the extra DNA in each cell! - Plant polyploidy can result in rapid speciation. o

Variation in Sexual Reproduction

Variation in Sexual Reproduction - Sexual reproduction typically involves a male and a female animal. - But what if mate-finding is very difficult? - Evolution has blurred the lines between male and female in some animals! Hermaphrodism - Organisms like the barnacle have fully developed male and female sexual organs. - This allows any 2 organisms to mate, reducing likelihood of incompatibility. - Both exchange and receive sperm, and both produce eggs Hermaphrodism - These nudibranch sea slugs are hermaphrodites, they exchange sperm and will both produce offspring. - Some species, like corals can self-fertilize. Sex Reversal - Sex reversal may act as an adaptation to ensure reproduction can still occur if the resident male dies. - Individuals that undergo sex reversal reproduce in both ways over their lives, carrying on a huge amount of their genes.

What happens to genes on far ends of the chromosome? + Variation ideas

What happens to genes on far ends of the chromosome? - Any map unit over 50% is considered genetically unlinked. - Crossing over occurs frequently. - At that distance, 50/50 chance of appearing in any given gamete. - Mapped by adding the recombination frequencies from crosses involving closer pairs of genes lying between the two distant genes. Combinations of Alleles: Variation for Natural Selection - Genetic variability is the raw material of natural selection. - All of what we've learned about so far (crossing over, independent assortment, recombination, degrees of dominance) increase genetic variability among offspring. - Selection pressure may act on these differences, driving evolution.

Plants have 3 basic "organs"

o Root system § Center tap root, Lateral roots, § Absorbs water and minerals through root hairs o Shoot system § Stems · Placement for leaves and sometimes for food storage • Leaves Main photosynthesis organ Veins carry water and nutrients o Reproductive Shoot § Flowers and fruits