BIOL2110 Problem Set 2 - 2020 PDF

Preview

Summary

Download BIOL2110 Problem Set 2 - 2020 PDF

Description

BIOL2110/6110 Genetics - Problem Set 2 1. On the basis of Mendel’s observations, predict the results from the following crosses with peas: (a) a tall (dominant and homozygous) variety crossed with a dwarf variety; 100% heterozygous tall (b) the progeny of (a) self-fertilized; 1:2:1 homozygous tall, heterozygous tall, homozygous dwarf (c) the progeny from (a) crossed with the original tall parent; 1:1 homozygous tall, heterozygous tall (d) the progeny of (a) crossed with the original dwarf parent. 1:1 heterozygous tall, homozygous dwarf

2. Mendel crossed pea plants that produced round seeds with those that produced wrinkled seeds and self-fertilized the progeny. In the F 2, he observed 5474 round seeds and 1850 wrinkled seeds. Using the letters A and a for the seed texture alleles, diagram Mendel’s crosses, showing the genotypes of the plants in each generation. Are the results consistent with the Principle of Segregation? Yes F1 A A a Aa Aa a Aa Aa F2 A a

A AA Aa

a Aa aa

3:1 = 5493:1831 3. A geneticist crossed wild, gray-colored mice with white (albino) mice. All the progeny were gray. These progeny were intercrossed to produce an F 2, which consisted of 198 gray and 72 white mice. Propose a hypothesis to explain these results, diagram the crosses, and compare the results with the predictions of the hypothesis. F1 G G g Gg Gg g Gg Gg F2 G g

G GG Gg

g Gg gg

Gray White

Observed 198 72

Expected 202.5 67.5

Chi-squared: 0.1 + 0.3 = 0.4  P>0.05 Thus difference is not significant, caused by chance 4. In pigeons, a dominant allele A causes a checkered pattern in the feathers; its recessive allele a produces a plain pattern. Feather coloration is controlled by an independently assorting gene; the dominant allele B produces red feathers, and the recessive allele b produces brown feathers. Birds from a true-breeding checkered, red variety are crossed to birds from a true-breeding plain, brown variety. (a) Predict the phenotype of their progeny. Checkered, red

(b) If these progeny are intercrossed, what phenotypes will appear in the F 2, and in what proportions? 9:3:3:1 Checkered red, Checkered brown, Plain red, Plain brown

5. In shorthorn cattle, the genotype RR causes a red coat, the genotype rr causes a white coat, and the genotype Rr causes a roan coat. A breeder has red, white, and roan cows and bulls. What phenotypes might be expected from the following matings, and in what proportions? (a) red  red; 100% red (b) red  roan; 1:1 red, roan (c) red  white; 100% roan (d) roan  roan. 1:2:1 red, roan, white 6. A researcher studied six independently assorting genes in a plant. Each gene has a dominant and a recessive allele: R black stem, r red stem; D tall plant, d dwarf plant; C full pods, c constricted pods; O round fruit, o oval fruit; H hairless leaves, h hairy leaves; W purple flower, w white flower. From the cross (P1) Rr Dd cc Oo Hh Ww  (P2) Rr dd Cc oo Hh ww, (a) How many kinds of gametes can be formed by P1? 32 (b) How many genotypes are possible among the progeny of this cross? 6561 (c) How many phenotypes are possible among the progeny? 32 (d) What is the probability of obtaining the Rr Dd cc Oo hh ww genotype in the progeny? 1/4096 (e) What is the probability of obtaining a black, dwarf, constricted, oval, hairy, purple phenotype in the progeny? 24/4096

7.

In the pedigrees below, determine whether the trait is more likely to be due to a dominant or a recessive allele. Assume the trait is rare in the population.

Re c e s s i v e

Do mi n a n t

8. The pedigree to the left shows the inheritance of a recessive trait. What is the chance that the couple III-3 and III-4 will have an affected child? 50%

9. The pedigree to the left shows the inheritance of a dominant trait. What is the chance that the offspring of the following matings will show the trait: (a) III - 1  III – 3 0% (b) III - 2  III – 4 50%

10. The pedigree below shows the inheritance of a recessive trait. Unless there is evidence to the contrary, assume that the individuals who have married into the family do not carry the recessive allele. What is the chance that the offspring of the following matings will show the trait: (a) III - 1  III - 12 = if III-1 is homozygous chances are 0%, if heterozygous 25% (b) II - 4  III - 14 = 0% (c) III - 6  III – 13 = 0% (d) IV - 1  IV – 2 = 0%...