Epistasis is the interaction between genes such that one gene influences or inte

Question

Epistasis is the interaction between genes such that one gene influences or interferes with the expression of another gene, leading to a specific phenotype. Use your knowledge of epistasis to determine the genotypes of offspring in the following crosses.

a. In laborador retrievers, pigment color is influenced by two genes. Gene A determines the type of pigment produced (black or brown) and gene B affects whether the pigment gets deposited in the hair shaft (no pigment produces a yellow dog).

If two heterozygous black laborator retrievers were crossed and offspring were produced in a ratio of 9 black dogs to 3 brown dogs to 4 yellow dogs, what are the genotypes of the offspring?

b. In freshwater snails, pigment color is influenced by two genes. If two heterozygous pigmented freshwater snails were crossed and offspring were produced in a ratio of 9 pigmented snails to 7 albino snails, what are the genotypes of the offspring?

Explanation / Answer

a. 9:3:4 is the ratio for recessive epistasis

lets say gene responsible for black colour is A and gene B responsible for hair shaft colour is C

according to question heterozygotes black labrodor retreiver crossed then, genotypes will be

AaCc X AaCc

offspring we get are

Those in bold are the 9 black dogs

cc is epistatic to mast the effect of A

therefore

3 brown dogs genotypes are- aaCC, 2aaCc

4 yellow dogs- aacc, AAcc, 2Aacc

b. this is a case of Duplicate recessive gene interaction (9: 7)

according to question heterozygotes pigmented freshwater snail crossed then, genotypes will be:

let say,

Gene pair ‘A’ – pigmented dominant over albino

Gene pair ‘B’ – Colour dominant over colourless

pigmented snail will occur only if two dominant gene will appear together otherwise it eill be an albino.

Homozygous recessive of either gene will produce an albino.

here cross will be between

AaCc X AaCc

offspring we get are

Here from the checkerboard all in bold will be pigmented because of Dominant gene.

While other 7 received atleast one of pair of receessive gene and resulted into albino.

AC Ac aC ac AC AACC AACc AcCC AaCc Ac AACc AAcc AaCc Aacc aC AaCC AaCc aaCC aaCc ac AaCc Aacc aaCc aacc

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