Question

Two mutant flies both have white eyes (red is the normal eye color) but were each isolated in different labs and therefore have been labeled white 1 (w1) and white 2 (w2). You cross a pure-breeding w1 fly to a pure-breeding w2 fly and the progeny consists of only flies with wild-type (red) eyes.
a) How can this result be explained?

b) Write out the full genotypes of the parents with respect to the mutant alleles and the genotypes of the progeny.

Answer 1

Answer:

A) The eye colour may be controlled by one or more genes, mutation lies in two different genes and has complemented each other.

B) Parent 1: w1w1 w2+w2+ Parent 2:w1+ w1+w2w2

Gametes: w1 w2+ and w1+w2

Offspring genotype: w1 w2+ w1+ w2

Explanation:

This condition may be because of complementary genes. When the presence of two or more genes are required for a particular trait and the absent of one of the genes affects the character, it is referred to as complementary genes. In this condition the wild type of fly have AA/BB type of gene and expression of both gene is responsible for red coloured eyes.

a. Mutation in any of the genes, affect the accumulation of red pigment in eyes and cause the eyes to be white colored. Given that two mutants W1 and W2 have white eyes but both have mutation in different genes. Suppose W1 has mutation in AA gene(genotype aaBB )and mutant W2 has mutation in BB gene (genotype AAbb).

b. Crossing between mutants give red colour eyes fly:

Parents AAbb x aaBB

​Gametes Ab aB

​Progeny AaBb

That is,

Parent 1: w1w1 w2+w2+ Parent 2:w1+ w1+w2w2

Gametes: w1 w2+ and w1+w2

Offspring genotype: w1 w2+ w1+ w2

​Result: progeny of mutant have both type of functional alleles (A and B), responsible for red colour of eyes. Thus the progeny will be with red colour eyes.