From the given data,
• The recessive allele s codes for small wings in drosophila.
• The s1 allele codes for normal wings.
• The gene with these alleles is X linked.
The genotype of small-winged males is sY and the genotype of homozygous wild-type females is s1 s1.
Cross between these two genotypes would have the following progeny:
sY x s1 s1
s s 1 s s 1 s 1 Y s 1 Y … all the F1 progeny have normal wings.
Both female progeny and male progeny have normal wings, as all carry the allele that codes for normal wings, which are dominant over the small wings.
Intercrossing the F1 progeny would result in the following progeny:
s s 1 x s1Y
ss 1 s 1 s 1 sY s 1 Y
Half of the female progeny would carry recessive allele, but express normal phenotype, since their genotype is s s1. Another ½ of the female progeny carry alleles that both code for normal wings.
Half of the male progeny express small wings, while the other half express normal wings.
Thus, only ¼ of the F2 progeny would express small wings.
Backcrossing F1 females with their father would result in the following progeny:
s s 1 x sY
ss ss 1 sY s 1 Y
Half of the progeny of each sex would have small wings.