Question

1) In cattle, there is no dominance between the alleles for red coat (W) and white coat (c). The heterozygote is intermediate or "roan" in color.

a) Give the genotypic and phenotypic ratios to be expected following a mating between two roan animals.

b) What are the expected genotypic and phenotypic ratios from a cross between a roan animal and a white one?

2) In cattle, the hornless condition (H) is dominant to that for the possession of horns (h).

a) A horned bull is mated to a hornless cow, which is heterozygous. What kind of offspring are to be expected and in what ratio?

b) If the cow is next mated to a hornless bull, which is also heterozygous, what is the chance that the first calf will have horns?

c) Assuming that the first calf has horns, what is the chance that the second calf will be hornless?

3) Very little hair is found on a Mexican hairless dog. A cross between a Mexican hairless dog and a dog with typical coat usually produces litters of pups in which half of the animals are hairless and half have hair. On the other hand, a cross between two Mexican hairless dogs produces litters in which two-thirds of the pups are hairless and one third have hair. However, in addition to these surviving puppies, some pups are usually born dead. These prove to be hairless, and they occur in about the same frequency as the live pups with hair. Offer an explanation for these observations. Using the letters "M" and "m" to represent the genotypes of the animals, diagram the crosses mentioned in this discussion.

4) In Guinea pigs, black fur ("A") is dominant to the albino condition ("a"), which produces white fur. A female from a homozygous black strain carries ovaries transplanted from an albino female. The albino female has received in turn the ovaries from the homozygous black animal.

a) What are the expected results when the black female is mated to a black male,
which has a white parent?

b) What results are to be expected if the albino female is mated to the same male?
Diagram the cross.

c) Suppose the black female used in the transplant study had a white parent.
Would this change your answers to parts (a) and (b) above? Explain.

5) In certain breeds of chickens, the allele "B" is responsible for black feathers whereas the contrasting allele "b" produces feathers that are white (except for flecks of black). Birds heterozygous for this pair of alleles have blue feathers. Another pair of alleles influences the shape of the feathers. "F" produces straight feathers whereas the contrasting gene form "f" results in the frizzled condition (twisted, brittle feathers). A bird heterozygous for this pair of alleles is mildly frizzled. Give the phenotypic ratios to be expected from each of the following crosses:

a) A black, frizzled hen x a white straight rooster

b) A white, frizzled hen x a blue, straight rooster

c) A blue, mildly frizzled hen x a white, frizzled rooster

d) A blue, mildly frizzled hen x a blue, mildly frizzled rooster

Answer 1

1) Genotype of for red coat cattle - WW.

  Genotype of for white coat cattle - cc.

Genotype of heterozygote roan color cattle - Wc.

a) Cross between roan color cattle Wc X Wc

Gametes formed W and c W and c.

Next generation

Male/Female	W	c
W	WW(red coat cattle)	Wc(roan coat cattle)
c	Wc(roan coat cattle)	cc(white coat cattle)

Genotypic ratio - 1WW : 2Wc : 1cc.

Phenotypic ratio - 1 red coat cattle :2 roan coat cattle :1 white coat cattle.

b) Cross between a roan animal and a white one - Wc X cc

Gametes formed W and c c and c.

Next generation

Male/Female	W	c
c	Wc(roan coat cattle)	cc(white coat cattle)
c	Wc(roan coat cattle )	cc(white coat cattle)

The expected genotypic ratio - 1:1( 2 Wc : 2 cc).

The expected phenotypic ratio - 1:1( 2 roan coat cattle : 2 white coat cattle)