In cross I we are treating F1 x dp se cross b and dp se x F

In cross I, we are treating F1 x dp se (cross [b] ) and dp se   x   F1 (cross [c]) as equivalent crosses, but in Drosophila that is generally a very bad idea! Why is it a bad idea in general and why will we be able to get away with it in cross I? (3 points)

Cross B is (F1 virgin females X dp;se males)

Cross C (dp;se virgin females X F1 males)

Solution

In Drosophila males, crossing over does not occur. Second, males have only one X chromosome, which their offsprings do not inherit. So, if Drosophila male is having a characteristic on the X-chromosome, then its offspring will not have the same.

Cross B is F1 virgin females X dp;se males

Result will be virgin males; females will also be virgin (because they are heterozygous).

Cross C (dp;se virgin females X F1 males)

Result: Males will be dp/se. They will inherit the characteristic of female parent.

Females will heterozygous wild type: dp/se in ratio 1:1. This is because F1 males are heterozygous. And they will transmit characteristic only to their female children, who have 2X chromosomes.