Question

6. a) Knowing what you know about the fur color and ear phenotype of our dogs in the previous question, what would happen if I crossed a diheterozygote with a dog homozygous recessive for ear shape and heterozygous for fur color.

b) What is the genotype of the diheterozygote?

c) What is the genotype of the dog heterozygous for fur color and homozygous recessive for ear shape?

d) What is the phenotypic ratio of the offspring?

Answer 1

a. Diheterozygote refers to the dog having heterozygous alleles for two phenotypes. In this question the two phenotypes are ear and fur colour. Let us assume the allele for Ear color is E and for fur is F. So the diheterozygote (Dog 1) will have a genotype of FfEe while the dog homozygous recessive for ear shape and heterozygous for fur color (dog 2) will have genotype Ffee. Now, let us consider the gametes produced from each. The diheterozygote will produce 4 gametes F, f, E, e while Dog2 will produce 3 gametes F, f and e.

So after mating we can have the following: Fe, fe, EF, Ef.

Punnett square of the following cross will be:

	Fe	fe	EF	Ef
Fe	FFee (Coloured fur, recessive ear phenotype)	Ffee (Coloured fur, recessive ear phenotype)	FFEe (Coloured fur, dominant ear phenotype)	FfEe (diheterozygote: Coloured fur, dominant ear phenotype)
fe	Ffee (Coloured fur, recessive ear phenotype)	ffee (double recessive)	FfEe (diheterozygote: Coloured fur, dominant ear phenotype)	ffEe (no fur color, dominant ear phenotype)
EF	FFEe (Coloured fur, dominant ear phenotype)	FfEe (diheterozygote: Coloured fur, recessive ear phenotype)	FFEE (Coloured fur, dominant ear phenotype)	FfEE (Coloured fur, dominant ear phenotype)
Ef	FfEe (diheterozygote: Coloured fur, dominant ear phenotype)	ffEe ( no fur color, dominant ear phenotype)	FfEE (Coloured fur, dominant ear phenotype)	ffEE (no fur color, dominant ear phenotype)

So we will get 4 different phenotypes after the mating.

b. Diheterozygote (Dog 1) will have a genotype of FfEe

c.Dog homozygous recessive for ear shape and heterozygous for fur color (dog 2) will have genotype Ffee

d. The phenotypic ratio of the offspring would be: 9:3:3:1 (as indicated by the colours of the Punnett square)

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