Question

In Drosophila, yellow body is due to an X-linked gene (Xy) that is recessive to the gene for gray body (X+). A homozygous gray female is crossed with a yellow male. If the F1 progeny are intercrossed, what proportion of the F2 progeny will be yellow?

Answer 1

In an X-linked recessive cross in Drosophila, the F2 generation will have a proportion of 3/8 yellow-bodied flies, resulting from the intercross of heterozygous gray-bodied female (X+Xy) and gray-bodied male (X+Y) from the F1 generation.

Step-by-step explanation:

In this X-linked recessive trait scenario in Drosophila, we need to calculate the proportion of yellow bodied flies in the F2 progeny resulting from an intercross of the F1 individuals. A homozygous gray-bodied female (X+X+) crossed with a yellow-bodied male (XyY) will produce F1 female offspring that are all heterozygous gray-bodied (X+Xy) and male offspring that are all gray-bodied (X+Y), because they inherit the dominant allele from their mother and the Y chromosome from their father. When these F1 progeny are intercrossed, the F2 progeny will be a mix of yellow and gray-bodied flies. The genotype ratio for the females will be 1X+X+:2X+Xy:1XyXy, and for the males, it will be 1X+Y:1XyY. Therefore, the proportion of yellow flies in the F2 generation will be 1/4 females (XyXy) and 1/2 males (XyY), resulting in an overall proportion of yellow-bodied flies being 3/8.