There are many wing mutations seen for Drosophila. You are studying a new mutati

Question

There are many wing mutations seen for Drosophila. You are studying a new mutation that produces crinkled wings.
a. When a true-breeding crinkled-wing fly is crossed with a true-breeding apterous (no wings) fly, all of the F1 progeny are wild type. The same results are seen for the reciprocal parental cross. What can you conclude about these mutations and the gene(s) that code for them? Justify your conclusions.
Since both lines are true-breeding, they are homozygous for their respective traits.
Both traits are on different genes because otherwise there would not be any wild type genes for those traits in the cross.
Since they are on different genes, it is possible to conclude that both lines are homozygous wild types for the traits they don’t express.

Both genes are recessive because the wild types gene from the other parent dominates in each case.

We are essentially breeding CCww flies and ccWW flies, where c and w are crinkle and wingless, and C and W are wild-type. All of the come out CcWw in which C and W are dominant, so all the flies express as a wild-type.

b. Two of the F1 flies were then crossed, producing a large F2 consisting only of wild type, crinkled and apterous flies in a 9:3:4 ratio. What can you conclude from the progeny of this cross? Justify your conclusions.

Explanation / Answer

Since both lines are true-breeding, you know they are homozygous for their respective traits.

AAbb x aaBB

AaBb-------------- wild type.
A and B are dominant

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