BIS 2B Lecture Notes - Lecture 12: Dihybrid Cross, Allele Frequency, Genotype Frequency

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fuchsiawhale832

23 Oct 2018

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UC-Davis

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Biological Sciences

Course

BIS 2B

Professor

Mark Schwartz; Sharon Strauss

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BIS 2B Lecture Notes - Lecture 11: Mendelian Inheritance, Allele Frequency, Tyrosinase

BIS 2B Lecture Notes - Lecture 12: Dihybrid Cross, Allele Frequency, Genotype Frequency

BIS 2B Lecture 13: Gene Flow to Natural Selection, Discussion 4

Document Summary

Imagine that you have three loci, each has two alleles that sort independently: yellow/green (y/y) peas; smooth/wrinkled (ss) peas; purple flowers/white flowers (pp) Take a true breeding yellow, wrinkled, white flowered plant and cross it to a true breeding green smooth purple one to make the f 1 . Now cross the f 1 "s to get an f 2. Green , smooth , purple flowered . Given allele frequencies for a dominant trait of 0. 6, with only a single recessive trait, what do you expect genotype frequencies at hardy-weinberg equilibrium (cid:262)(cid:625)aa(cid:626)=. (cid:546)6, (cid:262)(cid:625)aa(cid:626)=(cid:547)(cid:551), (cid:262)(cid:625)aa(cid:626)=(cid:544)6. F(cid:327)e(cid:326)ue(cid:300)cy o(cid:262) this t(cid:327)ait (cid:299)ust be (cid:544)-. (cid:544)6= . 84. X h y= (cid:552)(cid:545)% (cid:326)= (cid:262)(cid:625)x h (cid:626)=. (cid:543)(cid:551) p= (cid:262)(cid:625)x h (cid:626)=. (cid:552)(cid:545) (cid:262)(cid:625)x h x h (cid:626)= (cid:326) (cid:545) = (cid:625). (cid:543)(cid:551)(cid:626) (cid:545) = . (cid:543)(cid:543)6(cid:547) Hardy-weinberg equilibrium assumes: large (infinite) population, random mating, no gene flow from other populations, no new mutations, no natural selection! Mutation: the source of all novel genetic variation.

Related Questions

Problem A. You cross two homozygous parents: RRYY (round yellow) and rryy (wrinkled green) to produce an F1 generation. Round seeds are dominant, yellow seeds are dominant. You cross two F1s to produce the F2 generation. In the F2 generation, you find an individual with round yellow seeds. You do a testcross to find out the genotype of this âmysteryâ dominant/dominant phenotype. In the offspring of the cross, you find 1?2 have round yellow seeds and 1?2 have wrinkled yellow seeds.

1. Based on these data what was the genotype of the mystery F2?

Problem B. You carry out a dihybrid cross between a red-flowered rose with long pollen grains (A1A1 LL) and a white-flowered rose with round pollen (A2A2 l l). The flower color gene (A) shows incomplete dominance, and long pollen is completely dominant to round pollen. The genes for these traits are on different chromosomes so assort independently

2. What would be the phenotypes of the F1 generation?

3. What fraction of the F2 generation is expected to have red flowers and long pollen? (As always when traits are independent, what rule can you apply to save time?)

Problem D. In the example of epistasis presented in class, the agouti allele in mice (A) codes for striped hairs and is dominant to the allele for all black hairs (a). A loss-of-function allele for the pigment gene (b) produces no pigment and is recessive to the normal, dominant allele (B). The recessive allele at b masks the effect of the A gene. A dihybrid cross of AABB and aabb is carried out.

5. Name all of the genotypes in the F2 generation that can produce an albino (no pigment) phenotype.

Problem E. A cross is made between homozygous fruit flies that differ for eye color (the st gene) and

body color (the e gene). The F1 double heterozygote is shown below using chromosome notation.

st+ e

--------------------------------------

st e+

st = the recessive allele for scarlet eyes; st+ = the dominant wildtype allele for red eyes e = the recessive allele for ebony body; e+ is the dominant wildtype allele for gray body

6. Are the chromosomes shown in the genotype above in cis or trans configuration?

7. Based on this notation, what were the genotypes and phenotypes of the two parents of the F1? (Think carefully here...)

8. With what phenotype would you cross this F1 to measure recombination frequency?

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1. Characters that show a continuous range of variation, such as height and eye color, usually are controlled:

a.	by a single gene with two alleles that are codominant.

b.	by many genes with an additive effect.

c.	by epistatic interactions between two genes.

d.	mainly by the environment, with only a small genetic component.

2. In humans, red-green colorblindness is inherited as a sex-linked recessive trait. In order for a woman to be red-green colorblind, which of the following statements must be true.

a.	Her mother must be red-green colorblind.

b.	All of her brothers must be red-green colorblind.

c.	Her father must be red-green colorblind.

d.	All of the above statements must be true if a woman is red-green colorblind.

3. The x-ray crystallography data collected by Rosalind Franklin suggested to Watson and Crick that the:

a.	structure of DNA is a double helix.

b.	two strands of the DNA molecule are joined by hydrogen bonds between the bases.

c.	four bases within DNA pair in a specific way.

d.	two strands of the DNA molecule are joined by covalent bonds between the bases.

4. In the genetic code, _________ one amino acid.

a.	one nucleotide specifies

b.	two nucleotides specify

c.	three nucleotides specify

d.	four nucleotides specify

5. During Meiosis I, a homologous pair of chromosomes may not separate, resulting in daughter cells that have extra chromosomes or are missing chromosomes. This can lead to genetic disorders, including Down Syndrome. This phenomenon is called:

a.	independent assortment.

b.	nondisjunction.

c.	segregation.

d.	crossing over.

6. You are a human geneticist studying the incidence of retinitis pigmentosa in the residents of Tristan de Cunha, a group of small islands in the middle of the southern Atlantic Ocean. The allele for retinitis pigmentosa, which causes a form of blindness, is inherited as an autosomal recessive. You have determined that the frequency of this allele (r) in the population is 0.4 (40%). Using the principles of the Hardy-Weinberg rule, you would estimate the frequency of individuals who are heterozygous for this allele (Rr) in the population to be:

a.	0.16 (16%)

b.	0.24 (24%)

c.	0.36 (36%)

d.	0.48 (48%)

7. Natural selection acts at the level of the:

a.	phenotype.

gene.

c.	population.

d.	nucleotide.

8. You are working with pea plants, trying to recreate the experiments that Mendel performed. You are doing a dihybrid cross with a plant that is heterozygous for both seed shape and seed color, with the genotype RrYy. Which allelic combinations would you expect to find in the gametes produced by this plant?

a.	This plant would produce only RY and ry gametes.

b.	This plant would produce only RrYy gametes.

c.	This plant would produce RY, Ry, rY, and ry gametes.

d.	You cannot determine which gametes this plant can produce without knowing the genotypes of its parents.

9. Biochemist Erwin Chargaff found that in DNA there is a special relationship between the four bases that we now call Chargaff's rule. His observation was that, in an organism's genome the:

a.	percentage of A nucleotides = the percentage of T nucleotides, and the percentage of C nucleotides = the percentage of G nucleotides.

b.	four bases all occur in an equal frequency (25%) within each organism.

c.	percentage of A nucleotides = the percentage of G nucleotides, and the percentage of C nucleotides = the percentage of T nucleotides.

d.	genetic material is composed of proteins, not DNA.

10. During DNA replication:

a.	each strand of the double helix acts as a template for the synthesis of a new strand.

b.	the enzyme DNA polymerase adds nucleotides to the strand being synthesized.

c.	the bases A,C,G and T are required.

d.	All of the above are true of DNA replication.

11. During translation, amino acids are joined by peptide bonds to make polypeptides. The formation of these peptide bonds is catalyzed by:

12. If an allele (R) at a gene with two alleles shows complete dominance, individuals with the genotypes ______ will have the same phenotype.

a.	RR and rr.

RR and Rr

Rr and rr

d.	Each of the three possible genotypes will have a different phenotype.

mauvefox570

1.
In wolves, black coat color is recessive to the normal grey, andblue eye color is recessive to brown. A black-coated blue eyed malemates with a female who is heterozygous for both traits, and thereare 8 pups in the litter.
What are the expected genotoypes of the pups? what are the expectedphenotypes?

2.
A man and a woman both have normal color vision, and both havecolorblind fathers.
What proportion of their daughters would you expect to be colorblind?
What proportion of their sons?

3.
Assume that in the U.S. in 1960, the frequency of the autosomalrecessive Tay-Sachs disease among eastern European Jews was 1 per3600births.
What was the frequency of the Tay-Sachs allel in thispopulation?
In 1961, a woman of polish ancestry whose brother died of Tay-Sachsdisease marries a Jewish man of Hungarian ancestry. Assuming thatshe is a carrier, what is the probability that their first childwill have Tay-Sachs disease?

4. In fruit flies, black body (b) is recessive to normal body color(B). In a breeding study, a population of flies is allowed to mateat random. In the population, 3000 flies are homozygous for blackbody color, and 2000 flies are homozygous for the normalallele.
What is the frequency of each genotype in the F1 generation?
What would the proportion of phenotpyes be?
What is the frequency of the two alleles, B and b, in the F1generation?

5.
In peas, the dominant seed shape is round and the recessive iswrinkled(w). The dominant trait for pod color is green andrecessive is yellow (y). A plant with round seeds and green podsthat i heterozygous only for the color trait is crossed with aplant that has wrinkled seeds and yellow pods, and the resulting F1progeny are selfed(self fertilized).
Write out the P1 genotpes and the F1 and F2 genotypic andphenotypic ratios.
What proportion of the plants with green pods and round seeds fromthe F2 generation would you expect to be true breeding(i.e. produceonly plants with green pods and round seeds)?

Thank you

BIS 2B Lecture Notes - Lecture 12: Dihybrid Cross, Allele Frequency, Genotype Frequency

BIS 2B Lecture Notes - Lecture 11: Mendelian Inheritance, Allele Frequency, Tyrosinase

BIS 2B Lecture Notes - Lecture 12: Dihybrid Cross, Allele Frequency, Genotype Frequency

BIS 2B Lecture 13: Gene Flow to Natural Selection, Discussion 4

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