Question

In Drosophila, straight wings are dominant to curved wings (c), smooth eyes are dominant to sparkling eyes (spa), and tan body is dominant to ebony body color (e).
If flies that are heterozygous for all three traits are crossed, what proportion of the offspring would you expect to be heterozygous for all three traits?

Answer 1

Answer:

$\frac{1}{8}$

Explanation:

Straight wings are dominant over curved wings

Let Straight wings : H

curved wings : t

smooth eyes are dominant to sparkling eyes

let smooth eyes = H

spark ling eyes = t

tan body is dominant to ebony body color.

Again; Let tan body color be H

Let ebony color be t

If flies that are heterozygous for all three traits are crossed;

we have HtHtHt × HtHtHt

Then the selected trihybrid traits for the cross will be (HHH,HHt, HtH, Htt, tHH, tHt, ttH, ttt)

We will realize that from the punnet square in the diagram below, the proportion of the offspring would you expect to be heterozygous for all three traits (i.e HtHtHt) is asterisk in the punnet square and will be $\frac{8}{64}$

= $\frac{1}{8}$