Question

You conduct a cross between a true-breeding line of white fish and a true-breeding line of red fish. The F1 fish are all white. When the F1 fish are crossed to produce the F2 generation, the following data is obtained: White: 128 Red: 53 Pink: 42 Hypothesize a mode of inheritance for color in these fish.

Answer 1

In the F1 generation all fish are white colored. Which means the white is the dominant color and the red is the recessive color.

When two such F1 offspring are crossed, the F2 offspring are in the numbers---128 white, 53 red and 42 pink.

The total offspring are 223. The ration in a dihybrid cross has to be 9:3:3:1 under normal dominant and recessive inheritance. But we are getting the ratio as 9: 3: 4. ( 9 white, 3 pink, 4 red)

This is showing an epistatic inheritance. It is recessive epistasis. A recessive allele at epistatic  locus masks the inheritance of the gene at another locus. The gene for the white will express only when the epistatic locus has a dominant allele either homodominant (AA) or hetero dominant (Aa). If both are recessive, then the dominant trait can't be expressed, a recessive trait is expressed. In the absence fo the dominant allele at the epistatic locus, recessive allele is expressing which is red. Rest of the offspring are pink colored.

It is recessive epistatic inheritance.