Question

1. You have been asked to create a breed of cats that are hairless. After two years you have developed a strain of cats without hair. When you breed your cats to normal cats all the progeny are hairless. When you breed these to hairless progeny to each other you obtain 63 hairless and 22 cats with hair.

Part I using proper genetic terminology explain what has occurred.

Part II you have a friend who also has bred hairless cats, but when he mates his cats to normal cats all the cats are normal and when these progeny are mated to each other he gets 70 normal and 30 cats without fur. You are told by a friend that two genes are involved in the production of fur and that the relationship is one of reciprocal epistasis. Based on this please describe what the expected F1 and F2 outcomes would be if his cats are mated to yours. Please show the genotypes of the starting cats of the F1 and of the F2.

Answer 1

Representation:

Trait: Presence of hair.

· Hairless = dominant = HH (homozygous dominant), Hh (Heterozygous dominant).

Normal hairy = recessive=hh

Part 1:

Cross 1:

Hairless x normal (pure breeding)

	h	h
H	Hh	Hh
H	Hh	Hh

F1= All hairless

Cross 2: F1 x F1

Hairless x hairless (Heterozygous)

	H	h
H	HH	Hh
h	Hh	hh

Hairless = HH and Hh = ¾

Normal hair = hh =1/3

Phenotype Ratio =3:1

Part 2:

• Epistasis - Interaction of non -allelic genes. This factor is influence by the influence of loci on the gene. This value will change, if a single locus controls a gene, or if there is interaction between multiple loci of the gene.
• In the second case the roles of alleles are reversed due to reciprocal epistatic interaction.
• Thus, the dominant allele exhibits phenotype of recessive while the recessive allele exhibit the dominant phenotype.
• Thus, the allele which produces phenotype of hairless coat will be expressed as recessive. As all F1 are observed to be normal.
• While in F2 phenotype ratio is 3:1 for normal: hairless.