Question

You are doing a genetics experiment with fruit flies. In your first cross, you cross two true-breeding flies (P generation). The female parent is brown and wingless and the male parent is black with normal wings. All of the flies in the F1 generation are brown and have normal wings. In the following questions, please indicate the alleles associated with dominant phenotypes by uppercase letters and alleles associated with recessive phenotypes by lowercase letters. Assume the genes are not found on a sex chromosome. Indicate the color alleles as “F” and “f” the wing alleles by the letters “A” and “a”.

a. What are the genotypes of the flies in the P generation and the F1 generation?

b. You now take an F1 female and cross her to a true-breeding black, wingless male. What is the genotype of this male?

c. You count 1000 offspring from the cross described in Part B. If the wing and the color traits were not linked, what numbers of different offspring phenotypic classes would you expect?

Answer 1

The F2 expected ratio is 1:1:1:1 only when the genes are not linked. Linkage will produce a different offspring ratio.

Thanks