Bio212 Final

Haploid

During gamete production, only one copy is given to the gamete- this single set is called haploid

Mendel's Second Law

The Law of Independent Assortment

Probability Multiplication rule

"and" rule Probability of two independent events happening together: Multiply the probabilities of the individual events Tossing two coins- probability that both come up heads: 1/2 X 1/2= 1/4

Probability Addition rule

"or" rule The probability of an event that can occur in two different ways is the sum of the individual probabilities In F2, there are two ways to get a heterozygote: 1/4 + 1/4= 1/2 Result: 1:2:1 ratio of genotypes; 3:1 ratio of phenotypes

Conclusion

1. The plant being tested is homozygous 2. The plant being tested is heterozygous

Mendel's Postulates Heterozygous

2 alleles of a gene that are dissimilar

Mendel's Postulates Homozygous

2 alleles of a gene that are the same

Results

4 SS 2 Ss & 2 ss Homozygous Heterozygous

Heterosis

A cross between two different true-breeding homozygotes can result in offspring with stronger, larger phenotypes: "Hybrid vigor" or heterosis First discovered with corn by G.H. Shull

Gene and locus

A gene is a sequence on a DNA molecule that resides at a particular site on a chromosome- the locus- and encodes a particular character Different alleles of a gene separate during meiosis

A given gene may have more than ________

A given gene may have more than two alleles Example: Coat color in rabbits Multiple alleles increase the number of possible phenotypes Genes can have hundreds of alleles

Pleiotropic

A single allele can have multiple phenotypic effects: Pleiotropic Example: Allele for coloration pattern in Siamese cats; the same allele results in crossed eyes- both result from the same protein

Ratio of dominant to recessive in the F2 generation

About 3:1

Probability 0<P<1

All other events have a probability between 0 and 1

Punnett Square

Allele combinations can be predicted using a Punnett Square

Wild type

Allele present in most of the population. Other alleles are mutant alleles

Mendel's Second Law The Law of independent assortment

Alleles of different genes assort independently during gamete formation Doesn't always apply to genes on the same chromosome; but chromosomes do segregate independently

Probability P=1

An event is certain to happen, probability= 1

Mendel

Austrian monk His studies in physics and mathematics were a strong influence on his use of quantitative experimental methods. Over seven years, he made crosses with 24,034 plants

Inbreeding

Consanguinity Mating among close relatives Can result in offspring of low quality Close relatives tend to have the same recessive alleles Increases homozygosity at multiple loci (homozygous for many alleles) Sometimes want to have inbreeding= plants. Keep characteristic want to have. Open pollinated varietes heir loom varieties. Been crossed from a small number of individuals and maintained. Are now extremely high insest. Produce set of characteristics desired, but are far less resistant to disease and insects. Heterosis (heterozygote superiority)- produces heterozygous genes from two inbred strains

Sex determination varies among species Monoecious

Corn: Each adult produces both male and female gametes- monoecious (one house) Species can produce both male and female gametes (flat worms)

Mendel's first experiment

Crossed plants differing in just one trait (P) F1 generation are monohybrids The monohybrids were then allowed to self pollinate to form the F2 generation Mendel repeated this for all seven traits

Autosomes

Both sexes have two copies of all other chromosomes (beside sex chromosomes) called autosomes.

Human pedigrees

Can show Mendel's laws Humans have few offspring; pedigrees do not show the clear proportions that the pea plants showed Geneticists use pedigrees to determine whether a rare allele is dominant or recessive

Mendel's next experiment

Crossing peas that differed in two characters- seed shape and seed color True-breeding parents: SSYY- spherical yellow seeds ssyy- wrinkled green seeds

Mendel's next experiment Crossing the F1 generation Dihybrid cross

Crossing the F1 generation (all identical double heterozygotes) is a dihybrid cross

Multiple alleles for a single gene Rabbits

Dealing with 4 alleles Big C= dominant to everything else= dark gray All other alleles= chinchilla, light gray, point restricted, albino= recessive Light gray= chinchilla allele present in heterozygous state Point restricted= either homozygous or heterozygous in h allele Chinchilla and light gray are incompletely dominant to each other Point restricted= temperature sensitive allele= non functional at higher body temperature and functional at lower body temperature Albino= no color what so ever

Effects of genes and environment on phenotype Expressivity

Degree to which genotype is expressed in an individual People who do have a certain trait the degree to which it shows up and affects the individual

Gender determination and sex linkage

Determination is a genetic process, whether you are male or female is based on specific gene Differentiation= developmental process Primary= looking at the development of the plumbing and genitalia Secondary= puberty, hormones are turned on and gender maturation takes place

Mendel tested his hypothesis by doing test crosses

Determines whether an individual is homozygous or heterozygous for a trait by crossing it with the homozygous recessive Mendel crossed the F1 with known homozygotes (e.g., wrinkled or ss) Test that allows you to determine the genotype of an individual with dominate phenotype. Take individual with dominant phenotype X individual with recessive phenotype. Does the recessive trait show up? If so then the individual being tested is heterozygous

Mutation

Different alleles arise through mutation Rare, stable, inherited changes in the genetic material

Alleles

Different forms of a gene

Mendel's Postulates Law of Segregation

During formation of sex cells (eggs and sperm= gametes) unit factors separate (segregate) Each gamete gets one or the other but not both

Early inheritance worked under two assumptions about how inheritance works: Reciprocal crosses

Each parent contributes equally to offspring in reciprocal crosses (supported by experiments)

Each parent contributes ________ to offspring

Each parent contributes equally to offspring. (correct) Supported by reciprocal crosses, 1770s by Kolreuter

Results

F2 seeds from F1 plants 3 spherical seeds, 1 wrinkled seed

Mendel's characters were discrete and qualitative

For more complex characters, phenotypes vary continuously over a range- quantitative, or continuous, variation Quantitative variation is usually due to both genes and environment Most traits don't express themselves as a result of a single allele unlike discrete characteristics like Mendel's peas. Most traits are not that way, there are variation among the traits as a result of the genetic background. Quantitative traits are those caused by more than one gene You can't categorize these traits easily but you have to quantitatively analyze them since there are a lot of genes that influence height and some mutations also affect height

Trait

Form of a character (e.g., purple flowers or white flowers)

Mendel's next experiment Independent traits

Gametes could be SY, sy, Sy, or sY F2 would have nine different genotypes Phenotypes would be in 9:3:3:1 ratio

Mendel's next experiment Linked traits

Gametes would be SY or sy F2 would have three times more spherical yellow than wrinkled green

The "Particles" are now called ________

Genes

Dioecious organisms

In most dioecious organisms, sex is determined by differences in the chromosomes In many animals, sex is determined by a single sex chromosome, or by a pair Most mammals have 2 sex chromosomes, the x and y chromosome. The determination of gender is based on what is on the chromosome, not just if a female xx or a male xy

Quantitative trait loci

Genes that determine these complex characters Identifying these loci can help improve crop yields, understand disease susceptibility and behavior There are ways of identifying these genes (identify them in plants and animals) to find which genes influence a specific trait and be able to make those traits appear in their offspring's phenotype. Concordance: There is a very strong component that contributes to certain traits like alcoholism and people who have those receptors tend to have the specific receptors in their brains leading to the behavior (alcoholism)

Early inheritance worked under two assumptions about how inheritance works: Hereditary determinants

Hereditary determinants blend in offspring (not supported by experiments)

Pedigrees Recessive inheritance

Heterozygote (unaffected phenotype) mostly produce unaffected heterozygotes offspring when bread with unaffected mate

Codominance Blood type

Heterozygous for A or homozygous for AO= Type A Homozygous for B allele or heterozygous for BO= Type B Heterozygous for AB= Type AB= both types of antigens. Homozygous for O= Type O Type AB is recessive to everything else

Mendel's crosses: Second filial generation= F2

If F1 plants self pollinate, produce second filial generation or F2

Probability P=0

If an event cannot possibly happen, probability= 0

Mendel's next experiment Mendel's question

Mendel asked whether, in the gametes produced by SsYy, the traits would be linked, or segregate independently

How are incomplete dominance and codominance different?

Incomplete- looked at on the phenotypical level. Blue and yellow alleles on budgies are being expressed equal= codominance on molecular level but incomplete dominance at phenotypical level

Hereditary determinants blend in the offspring

Incorrect. It was thought that once hereditary elements had blended they could never be separated. Gregor Mendel's studies refuted this

Heterozygous

Individuals have two different alleles (e.g., Ss)

Reciprocal crosses yield the same results

It made no difference which parent contributed pollen The idea that each parent contributes equally was supported

Environment also affects phenotype

Light, temperature, nutrition, etc., can affect expression of the genotype Siamese cats and certain rabbit breeds- the enzyme that produces dark fur is inactive at higher temperatures Vp=Vg+Ve+COV Environmental effects: Temperature sensitive, nutrition and human height- people were much shorter in the medieval ages from poor nutrition

Polymorphic

Locus with wild-type allele present less than 99% of the time is polymorphic

When there is a rare recessive phenotype in a family, there is usually _______

Marriage of relatives If a recessive allele is rare in the general population, it is unlikely that two people that marry will both carry it unless they are related (e.g., cousins)

1900

Meiosis had been observed Three plant geneticists realized that chromosomes and meiosis provided a physical explanation for Mendel's results

Gamete vs. zygote

Mendel also concluded that each gamete contains only one particle (or unit), but the zygote contains two- because it is produced from the fusion of two gametes

Particulate theory

Mendel proposed that the heritable units were discrete particles Each plant has two particles for each character, one from each parent

Pedigrees Dominant inheritance

Most dominate traits are heterozygous

Blending theory

Not supported by Mendel's crosses

Character

Observable physical feature (e.g., flower color)

Mendel's mathematical analyses

One of Mendel's contributions to genetics was the use of mathematical analyses The rules of statistics and probability His analyses revealed patterns that allowed him to formulate his hypotheses Probability calculations and Punnett squares give the same results

Mendel's Postulates Disimilar pairs can be present

One tall, one dwarf form of that gene One will be expressed, the other is masked

Mendel's first experiment Recessive traits

One trait of each pair disappeared in the F1 generation and reappeared in the F2 generation

Mendel's next experiment

Parental (P) generation SSYY X ssyy F1 generation SsYy F1 Gametes SY Sy sY sy F2 generation: Yellow and round(SY)= 9/16, Green and round (Sy)= 3/16, Yellow and wrinkled (sY)= 3/16 Green and wrinkled (sy)= 1/16

Heritable trait

Passed from parent to offspring

Effects of genes and environment on phenotype

Penetrance Expressivity

Epistasis

Phenotypic expression of one gene is influence by another gene Example: Coat color in Labrador retrievers Allele B (black) dominant to b (brown) Allele E (pigment deposition) is dominant to e (no pigment deposition- yellow) A modification or masking of one phenotype of one gene by another gene

Phenotype

Physical appearance of an organism (e.g., spherical seeds).

Method

Plant a true-breeding spherical seed- Parental (P) seed Plant a true-breeding wrinkled seed Parental (P) seed Seeds grow into plants and produce pollen- Parental (P) plants F1 seeds are formed and grown into F1 plants F1 plant self-pollinates

Mendel's crosses: Parental generation=P

Pollen from one parent was transferred to the stigma of the other parent Parental generation=P

Dihybrid crosses

Probability that F2 seed will be spherical is 3/4=Probability of heterozygote + probability of homozygote: 1/2+1/4= 3/4 Joint probability that a seed will be spherical and yellow: 3/4 X 3/4= 9/16

Effects of genes and environment on phenotype Penetrance

Proportion of individuals with certain genotype that show the phenotype An individual carries an allele that is supposed to cause a trait but it doesn't show up Should show a trait but they don't Why don't they? The environment can contribute other alleles can act and cancel out that trait. Other alleles of other genes can minimize the effects of dangerous alleles

Mendel's new theory of inheritance

Published in 1866, but was largely ignored Most biologists at the time were not used to thinking in mathematical terms Even Darwin missed the significance of Mendel's work

Mendel's crosses: First filial generation= F1

Resulting offspring First filial generation or F1

Mendel's next experiment Results Recombinant phenotypes

Results indicated new combinations called recombinant phenotypes

Method

S_ X ss = SS X ss Ss X ss

Mendel's first experiment Monohybrid cross

Self pollination Forms F2 generation

Incomplete dominance

Some alleles are neither dominant nor recessive- a heterozygote has an intermediate phenotype: Incomplete dominance Example: Snapdragons Two alleles blend in the offspring. Neither one has a recessive or dominant relationship Example: Cross yellow budgie and blue budgie= green budgie offspring Intercorss F1: Green budgie X green budgie= 1/4 yellow; 1/2 green; 1/4 blue

Sex determination varies among species Dioecious

Some plants and most animals are dioecious (two houses)- male and female gametes are produced by different individuals Species cannot self fertilize and produce both male and female gametes, but only one or the other

Mendel's next experiment F1 Generation

SsYy All spherical yellow

Genotype

The genetic makeup (e.g., Ss) Spherical seeds can be the result of two different genotypes- SS or Ss

Conclusion

The hypothesis is rejected. There is no irreversible blending of characteristics, and a recessive trait can reappear in succeeding generations

Mendel looked for well-defined, true-breeding traits

The observed trait is the only one present for many generations

Hypothesis

The progeny of a test cross can reveal whether an organism is homozygous or heterozygous

Genome

The totality of all genes in an organism is the genome

Mendel's first experiment Dominant trait

The trait that appears in the F1 generation is the dominant trait

Mendel's First Law The Law of Segregation

The two copies of a gene separate when an individual makes gametes When the F1 self-pollinates, there are three ways to get the dominant trait (e.g., spherical), but only one way to get the recessive (wrinkled)- resulting in the 3:1 ratio

Diploid

The two copies of heritable unit in an organism

Mendel's Postulates Alleles

There are different 'flavors of unit factors for particular traits (tall vs. dwarf are types of gene or unit factor for plant height. Alleles.

Mendel's Postulates Unit Factors

Traits are controlled by discrete 'unit factors' (genes) Unit Factors are present in pairs (concept of diploid before anyone had ever seen chromosomes)

Homozygous

True-breeding individuals have two copies of the same allele- they are homozygous for the allele (e.g., ss)

Codominance

Two alleles at one locus produce phenotypes that are both present in the heterozygote Example: ABO blood group system- three alleles at one locus Two alleles are expressed at equal levels

The true-breeding plants in the P generation had

Two identical copies of the particle (gene) for each character Example: Spherical SS; wrinkled ss gametes from SS will have one S gametes from ss will have one s offspring (F1) will be Ss S is dominant; s is not expressed in F1

Hypothesis

When two strains of peas with contrasting traits are bred, their characteristics are irreversibly blended in succeeding generations

Mendel worked with the

garden pea He could control pollination and fertilization- and be sure of the parents of offspring Available, short life span from seed to seed. Produce large numbers of offspring, easily grown/cultured, different strains= different reproducible characteristics Peas= self fertile. Cross with themselves. Control from one plant to another

Mendel's Postulates Dominant

gene expressed

Mendel's Postulates Recessive

gene masked

True-breeding strains

were isolated by inbreeding and selection He concentrated on seven traits