Unit 5: Heredity

An event that is certain to occur has a probability of ____ , while an event that is certain not to occur has a probability of ____.

-1 -0

Review meiosis. When does crossing over occur?

-prophase I

What are two things that can be determined from a karyotype?

-screen for defective chromosomes -abnormal number of chromosomes

How does a somatic cell compare to a gamete in terms of chromosome number?

-somatic has 46 (diploid, 2n) -gamete has 23 (haploid, n)

What are the differences between mitosis & meiosis?

mitosis -enables multicellular animal/plant to arise from a single cell -1 DNA replication -1 division -2 identical daughter cells -2n meiosis -produces gametes or spores, reduce number of chromosomes -1 DNA replication -2 division -4 (haploid, different) -n

Name & describe three human sex-linked disorder.

-duchenne muscular dystrophy (rec): weakening of muscles & coordination -hemophilia (rec): blood clotting doesn't work properly -color blind (rec): mild disorder

Explain Mendel's law of independent assortment.

-each pair of alleles segregates into gametes independently -2 or more genes assort independently-each pair of alleles segregates independently of each other pair of alleles

What occurs in nodisjunction?

-error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other

In probability, what is an independent event?

-events, whose occurrence don't depend on any other event

In humans, how has the term sex linked gene been historically modified?

-few Y-linked genes, most on X, so called X-linked genes

Where are the gametes of an animal produced? Be specific as to male & female gametes.

-gametes develop from specialized cells called germ cells in the gonads -ovaries in females & testes in male

Explain epistasis.

-gene interaction, where phenotypic expression of one gene at one locus alters that of a gene of a second locus

What is the definition of a sex-linked gene?

-gene located on either sex chromosome

What is pleiotropy? Explain why this is important in disease like cystic fibrosis & sickle-cell disease.

-genes can have multiple effects on a phenotype -responsible for multiple symptoms associated with hereditary diseases

Alfred H. Sturtevant, a student of Thomas Hunt Morgan, used assumptions from observations of crossovers to map genes. What is a linkage map?

-genetic map based on recombination frequencies

Are the resultant daughter cells of meiosis I haploid or diploid?

-haploid

What is a Barr body? Why do human females show a Barr body in their cells?

-inactive X in each cell of a female condenses into a compact Barr body, inside the nuclear envelope -so that the cells of females and males have the same effective dose (one copy) of most X-linked genes

What are linked genes? Do you think genes sort independently?

-def: genes located near each other on the same chromosome, tend to be inherited together in genetic crosses -don't sort independently, but rather are transmitted as a unit

Explain how incomplete dominance is different from complete dominance & give an example of incomplete dominance.

-def: neither allele is completely dominant -ex: red x white snapdragons, F1 is pink

State the addition rule & give an original example.

-def: prob that any one of the 2 or mutually exclusive events will occur is calculated by adding their indv prob -ex: F2 as heterozygote, 1/4 +1/4 = 1/2

State the multiplication rule & give an original example.

-def: to determine this probability, we multiply the probability of one event by the prob of the other event -ex: 2 dices getting 1, 1/6 x 1/6 = 1/36

What is a map unit?

-distance btwn genes -defining map unit as equivalent to a 1% recombination frequency

Thomas Hunt Morgan selected Drosophila melanogaster as his experimental organism. List at least three reasons the fruit fly is an excellent subject for genetic studies.

-1) single mating produces 100s of offspring -2) new generation every 2 weeks -3) 4 pairs of chromosomes, distinguishable with a light microscope

If a man with type AB blood mates with a woman with type O blood, what blood types would you expect in the children?

-1/2 type A (IAi), 1/2 type B (IBi)

Describe all four of Mendel's concept & put an asterisk on concepts that can be observed during meiosis.

-1st concept: alt versions of genes account for variation in inherited characteristics -2nd concept: for each character, an organism inherits 2 copies (alleles) of a gene, one from each parent -3rd concept: if two alleles at a locus differ, the dominant alleles determines the phenotype -*4th concept (law of segregation) two alleles for a heritable characteristic segregate during gamete formation & end up in dif gametes

Now study the chromosomes in anaphase I & telophase I. How many chromosomes are in each cell at the end of the first meiotic division? ________

-3

How many chromosomes are in human cells? ______

-46

A female is a carrier for color blindness & mates a male with normal vision. What is the probability that they have a son who is color blind?

-50% chance that son will have disorder -50% chance daughter will be carrier

How many chromosomes does the cell above have? ________ How many homologous pairs? _________ How many chromatids? __________ Is this cell haploid or diploid? _________

-6 -3 -12 -diploid

YyRr x YyRr punnet square, phenotypic ratio

-9:3:3:1

Complete the ABO blood type chart.

-A has triangle -B has circle -AB has triangle & circle -O has none

Describe these genetic disorders. a. Cystic fibrosis b. Sickle-cell disease c. Achondroplasia d. Huntington's disease

-CB (rec): chloride transport channels are defective or absent in the plasma membranes of affected, resulting in an abnormally high concentration of extracellular chloride, which causes the mucus that coats certain cells to become thicker & stickier than normal -sickle (rec): substitution of amino acid, deformed blood cells -dwarf (dom): form of dwarfism -Huntington (dom): degeneration of nervous system, irreversible & fatal

What are the strengths & weaknesses of each fetal test?

-CVS: faster & can be preformed earlier in the pregnancy, no amniotic fluid -a: gets fetal cell & amniotic fluid, but is slower

When Thomas Hunt Morgan mated a white-eyed male fly with a red-eyed female, he came to the startling conclusion that the trait for eye color was located on the chromosome that determines sex. Show this cross by going through the three generations.

-P: female with red eyes x mutant white-eyed male -F1: all offspring had red eyes, wild allele is dominant -F2: typical Mendelian ratio of 3:1, but all white-eyed flies were male, therefore eyecolor is linked to sex

Define the following terms. Then consider your own family. Which generation would your mother's grandparents be? Your mother? You? P generation F1 generation F2 generation

-P: true breeding parents (mom's grandparents) -F1: hybrids (mother) -F2: second filial generation (me)

In pea plants, T is the allele for tall plants, while t is the allele for dwarf plants. If you have a tall plant, demonstrate with a testcross how it could be determined if the plant is homozygous tall or heterozygous tall.

-TT x tt = results in heterozygous -Tt x tt = 50% are short

There are several variations in the way sex is determined in different species. Look at the diagram & describe all four.

-X-Y: mammals, sex of the offspring depends on whether the sperm cell contains an X or Y chromosome -X-0: insects, only one sex chromosome, females are XX male are X0, sex of offspring determined whether sperm cell contains an X chromosome or none -Z-W: birds & fishes & insects, sex chromosomes present in egg, females ZW & male ZZ -haplo-diploid: bees & ants, no sex chromosomes in bees & ants, females are fertilized male are unfertilized

For these human aneuploidies give the sex & symptoms. XXY XXX XO XYY

-XXY: male (Klinefelter), have male organs, abnormally small testes, sterile, breast enlarged, female characteristics -XXX: female (trisomy X), healthy, slightly taller than average, risk for learning disabilities, fertile -XO: female (Turner), phenotypically female, but sterile due to lack of maturation in sex organs; normal intelligence -XYY: male, taller than average

Explain how gametes are derived for the following cross. YyRr x YyRr

-YR, Yr, yR, yr

a. What is the F2 phenotypic ratio? ___________________ , genotypic ratio? _____________ b. Which generation is completely heterozygous? ________ c. Which generation has both heterozygous & homozygous offspring? _________

-a. 3:1, 1:2:1 -b. F1 -c. F2

The notions for wild type & mutant traits follows some accepted conventions. Notate the following genotypes for a female fruit fly. a. fly with homozygous for red eyes b. fly with heterozygous for red eyes c. fly with homozygous for white eyes

-a. Xw+Xw+ -b. Xw+Xw -c. XwXw

Your study of plants this year will include knowing that they exhibit alternation of generations. a. What does this mean? b. What are the two generations? c. Which generation is haploid, & which is diploid?

-a. alt. of meiosis & fertilization (d & h stage) -b. sporophyte & gametophyte -c. h= gametophyte, d= sporophyte

Define the following terms. a. gene b. locus c. gametes d. male gamete e. female gamete f. somatic cells g. genome h. asexual reproduction i. sexual reproduction

-a. gene: hereditary units -b. locus: a gene's specific location along the length of a chromosome (latin meaning "place") -c. gametes: reproducing cells (human=23) -d. male gamete: sperm -e. female gamete: egg -f. somatic cells: all cells of the body except the gametes (human=46) -g. genome: cell's endowment of DNA, its genetic info -h. asexual reproduction: single indv is the sole parent & passes copies of all its genes to offspring w/o fusion of gametes -i. sexual reproduction: 2 parents give rise to offspring, that have a unique combo of parents gene

Explain how Mendel's simple cross of purple & white flowers did the following: a. refuted blending b. determined dominant & recessive characteristics c. demonstrate the merit of experiments that covered multiple generations

-a. no blending bc no light purple flowers only white or purple -b. if heterozygous/F1 gen, purple always masked white -c. basic patterns of inheritance, law of segregation & indp assortment, see outcome generationally & over time, recessive in F2

Explain the law of independent assortment.

-alleles of genes on non homologous chromosomes assort independently during gamete formation

What causes Down syndrome? What are four characteristics of Down syndrome?

-aneuploid condition, from extra chromosome 21 (also called trisomy 21) -characteristic facial features, short stature, correctable heart defects, developmental delays

Explain each of the following terms. aneuploidy monosomy trisomy polyploidy

-aneuploidy: (20% egg, 9% sperm) chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number -monosomy: diploid cell that has only one copy of a particular chromosome instead of the normal two -trisomy: diploid cell that has three copies of a particular chromosome instead of the normal two -polyploidy: chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division

Which type of reproduction will result in genetically identical offspring? __________________

-asexual

What is the mode of inheritance for this pedigree? Justify your response by citing evidence from the pedigree.

-attached earlobe is recessively inherited -explained by heterozygous parents having a ff daughter

How does the chromosome theory of inheritance provide a physical explanation for Mendelian inheritance?

-bc behavior of chromosomes during meiosis can account for the laws

Explain why the dihybrid cross, has four yellow dogs instead of the three that would have been predicted by Mendel's work.

-bc dom allele E results in the deposition of either black/brown pigment, if lab is homozygous recessive ee then regardless of genotype it is yellow -E/e gene is epistasis to B/b gene

Describe what you think is medically important to know about the behavior of recessive alleles.

-bc many genetic disorders are inherited genetically -be important to know if you are a carrier & have a change of having children with a disease

In the 1800s the most widely favored explanation of genetics was "blending". Explain the concept of blending & then describe how Mendel's "particulate" (gene) hypothesis was different.

-blending: idea that genetic material contributed by parents was mixed like paint (blue + yellow = green) -particulate: inheritance, parents pass discrete heritable unites-gene-that retain separate identities in offspring

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a dog. bone cell_______ sperm_______ haploid cell_______ somatic cell_______ zygote_______

-bone cell: 78 -sperm: 39 -haploid cell: 39 -somatic cell: 78 -zygote: 78

What are the symptoms of phenylketonuria (PKU)? How is newborn screening used to identity children with this disorder?

-cannot metabolize amino acid phenylalanine -can cause severe intellectual disability -screening such as biochemical test can identify the disorder, then special diet for children

What is the difference between a character & a trait? Explain using an example.

-character: heritable feature such as hair color -trait: each variant for a character, such as brown or blonde hair

What other organelle has its own genes? These are extranuclear genes.

-chloroplasts & plastids

Explain the physical events of crossing over.

-crossing over: a genetic rearrangement between nonsister chromatids involving the exchange of corresponding segments of DNA molecules, begins during pairing and synaptonemal complex formation, & is completed while homologs are in synapsis; chiasma exists at the point where a crossover has occurred

Compare & contrast codominance with incomplete dominance.

-def (co): two alleles each affect the phenotype in separate, distinguishable ways -ex: red x white flower = red & white flower

What is a karyotype? How is it prepared?

-def: a display of condensed chromosomes arranged in pairs; complete set of metaphase chromosomes in the cells of a species; sorted by long to short, centromere location & etc -prepared from isolated somatic cells, which are treated with a drug to stimulate mitosis & then grown in culture for several days; an image of the chromosomes is displayed on a computer monitor & a digital software is used to arrange them in pairs

What are alleles? Give an example.

-def: any alt. versions of a gene that may produce distinguishable phenotypic effects -ex: freckles

An important idea to understand is that new alleles arise by changes in the DNA or mutation, but genetic diversity occurs when the deck is simply reshuffled. So, there are three ways that sexually reproducing organisms "shuffle the deck". Explain how this increases diversity. independent assortment of chromosomes crossing over random fertilization

-independent assortment of chromosomes: random orientation of pairs of homologous chromosomes at metaphase of Meiosis I -crossing over: DNA molecules of non-sister chromatids are broken & are rejoined to each other, produce collection of gametes differing greatly in their combos from parent -random fertilization: random nature of fertilization

Cells that have only one of each homologous pair are said to be haploid. Cells that have two of each homologous pair are said to be diploid. For each of the following, is the cell haploid or diploid? liver zygote somatic gamete skin stem egg sperm

-liver: 2n -zygote: 2n -somatic: 2n -gamete: n -skin: 2n -stem: 2n -egg: n -sperm: n

By what process are gametes produced? ____________

-meiosis

Looking at the three types of sexual life cycles. Plants have a life cycle that involves spores, which form as a result of _____________ so these spores are haploid. Both haploid & diploid cells can divide by mitosis. However, meiosis begins with cells that are _________________, & as a result of meiosis, daughter cells are formed that are always ____________________. These cells can be gametes (animals) or spores (plants).

-meiosis -diploid -haploid

Although you inherited one chromosome of each pair from your mother and your father, you have inherited a group of genes from your mother only. What genes are these?

-mitochondrial DNA

The figure shows metaphase I. How is the arrangement of chromosomes different from the metaphase of mitosis?

-mitosis: indv chromosomes line up at metaphase plate -meiosis: pairs of homologous chromosomes line up at metaphase plate

Explain the difference between a monohybrid cross & a dihybrid cross?

-mono: heterozygous for one particular character being followed in the cross -di: individual heterozygous for 2 characteristics being followed in the cross

Explain what is meant when a gene is said to have multiple alleles. Blood groups are an excellent human example of this.

-most genes exist in more than 2 allelic forms

Dominant alleles are not necessarily more common than recessive alleles in the gene pool. Explain why this is true.

-natural selection determines how common an allele is in a gene pool -ex: having 6 fingers is dominant to 5, but is less common

Using the terms norm of reaction and multifactorial, explain the potential influence of the environment on phenotypic expression.

-norm: range of phenotypic possibilities for a genotype due to environmental influences -multi: can be influenced by genetic & environment -multifactorial characters follow a norm of reaction, a gradient/range; multiple things affect these traits, multiple genes and the environment. ex skin color is affected by genetics but also environmental factors such as sun intensity, sunscreen/no sunscreen

X inactivation maintains the proper gene dosage. How is the X chromosome inactivated?

-occurs randomly and independently in each embryonic cell present at the time of X inactivation, in a process called methylation

Explain what is meant by homologous chromosomes.

-pair of chromosomes of the same length, centromere position, and staining pattern -control the same inherited character (ex: hair color) -NOT identical

One of the keys to success for Mendel was his selection of pea plants. Explain how using pea plants allowed Mendel to control mating; that is how did this approach let Mendel be positive about the exact characteristics of each parent?

-pollen producing organs (stamens) & egg bearing organ (carpel) usually self-fertilizes -allowing him to cross/self fertilize -distinct heritable characteristics

Quantitative variation usually indicated polygenic inheritance. What is a good example of this?

-quantitative: measurable phenotype, depend on gene & environment -polygenic: additive effect of two or more genes on a single phenotypic characteristic -ex: skin color & height, bc characteristics vary in population & gradients along a continuum

If two genes are linked on the same chromosome, we call this combination the parental combination. These genes will be transmitted as a unit and will not sort independently. However, during meiosis, crossing over occurs between homologous chromosomes, and the linked genes can become "unlinked." In general, the farther two genes are from each other along the chromosome, the more often they will come "unlinked." Genetic recombination is the process during which linked genes become unlinked. What do geneticists call the offspring that show these new combinations?

-recombinants

Distinguish between sex chromosomes & autosomes. How many of each are found in human cells?

-sex chromosomes: determine an indv's sex (X & Y), 2 in human cells -autosomes: not sex chromosomes, 22 in human cells

What is the SRY gene? Where is it found, & what does it do?

-sex determining region of Y chromosome, required to develop testes

During Meiosis I, homologous chromosomes separate. What separates during Meiosis II?

-sister chromatids

In sexually reproducing organisms, why are there exactly two chromosomes in each homologous pair?

-somatic cells in a diploid organism have 2 sets of chromosomes, one set inherited from each parent

In meiosis, the DNA is replicated during interphase followed by two division. The first division is meiosis I. Study the events of prophase I and explain these terms. synapsis chiasmata

-synapsis: pairing & physical connection of duplicated homologous chromosomes -chiasmata: the point where crossover occurred, X shaped

Why can you say that all calico cats are females?

-tortoiseshell gene is on the X chromosome, & the tortoiseshell phenotype requires the presence of two different alleles, one for orange fur & one for black fur -only females can have both alleles, bc only they have two X chromosomes

Explain the law of segregation.

-two alleles for each gene separate during gamete formation

In the pedigree you just completed, explain why you know the genotype of one female in the third generation but are unsure of the other.

-unsure of the other bc she can be heterozygous or homozygous dominant, can only find out genotype by doing test cross

A number of genes will cause a variation in phenotype, depending on whether the gene came from the father or the mother. This variation occurs because of genomic imprinting. Explain genomic imprinting.

-variation in phenotype depending on whether an allele is inherited from the mother or father

Just a few years ago, biologist & medical personnel were surprised to learn that fetal cells can escape & enter the mother's blood. How can these cells be used in fetal testing?

-very few are present, cells can be cultured & tested, fetal DNA can be analyzed

"Why sex?" Any individual passes on more of its gene through asexual reproduction, so there must be some advantage to sexual reproduction, as it is almost universal among animals. Under what conditions is sexual reproduction most advantageous & why?

-when there are environmental changes, if some members can cope effectively bc of their mutations, then at least some will survive & pass on the helpful genes

Label the allele for both purple & white flower color, a homologous pair, & the lo us of the flower color gene. What is the difference between the nucleotide sequences of the purple flower allele compared to the white flower allele? Circle the allele which does not produce a function gene product.

-white allele has no functional protein being made

What unusual result suggested that the eye-color trait is located on the X chromosome?

-white eyed trait only appeared in males during F2

What is the probability that a couple will have a girl, a boy, & a boy in this specific order?

1/2 x 1/2 x 1/2 x 1/2 = 1/16

Use the figure below, which is from Figure 15.10. It shows the results of a cross between a fruit fly that is heterozygous for a gray body with normal wings, and a fruit fly that has a black body with vestigial wings. Because these genes are linked, the results are not what might have been predicted. Show the phenotypes and number of each type of offspring. Indicate which offspring are there combinants and which are the parental type. Finally, calculate the map distance between the two genes. Show all your work here.

391 recombinants/ 2,300 total x 100 = 17 % since frequency of recom is 17%, 2 genes are 17 map units apart