You cross two true-breeding strains of fish, opaque fish and clear fish. All the

Question

You cross two true-breeding strains of fish, opaque fish and clear fish. All the F1 progeny are opaque. Crossing two F1 opaque fish gives you F2 progeny in the ratios 64 opaque : 23 shiny : 30 clear. 10A) This cross can be explained by which of the following assignments of phenotype to genotype?

a) A/-; B/- opaque; a/a; B/- shiny;  A/-; b/b clear; a/a; b/b shiny

b) A/-; B/- opaque; a/a; B/- shiny; A/-; b/b opaque;  a/a; b/b clear

c) A/-; B/- opaque; a/a; B/- opaque; A/-; b/b clear; a/a; b/b shiny

d) A/-; B/- opaque; a/a; B/- shiny; A/-; b/b clear; a/a; b/b clear

10B) Given the genotype you picked in 12A, what is the relationship between the A and B genes? .

a) The A and B genes complement .

b) a is recessive epistatic to B .

c) b is recessive epistatic to A .

d) Both A and B genes determine fish coloration; no interaction between the genes

Explanation / Answer

10 A) Ans will be option (d) A/-; B/- opaque; a/a; B/- shiny; A/-; b/b clear; a/a; b/b clear

10 B) Ans will be option (c) b is recessive epistatic to A

Explanation: Epistasis can be described by a type of gene interaction where the expression of one gene can be modified or masked by another gene at distinct locus. Here the phenomena is Recessive epistasis where complete dominance is seen at both A and B gene pairs, but when one gene (B) is in homozygous recessive condition then it is epistatic to the other gene (A).

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