3 You caught a Drosophila female with red normalshaped compo

#3: You caught a Drosophila female with red normal-shaped compound eyes (wild type) in wild. This female had been apparently mated with a male with an unknown genotype before you caught her. After keeping her in a culture medium, she laid about 200 eggs. About 10 days later, adult flies came out. They are:

Eye color

Eye shape

Females

Wild-type red

All malformed small eye

Males

50% Wild-type red

50% White (no eye pigment)

All normal-shaped

Infer the genotypes of this female and the male that mated with this female in wild.

PLEASE EXPLAIN, I DON\'T UNDERSTAND THIS CONCEPT.

Solution

The fact that all progeny of a particular sex had only one shape of eyes suggests that the trait is sex-linked. Therefore, the female parent must have had the genotype: RrX^sX^s, and the male parent must have had the genotype: RrX^SY.

(R denotes the wild-type dominant allele for red eye color, r denotes the mutant, recessive allele for white eye color; X^s denotes the X-linked recessive wild-type allele for normal-shaped eyes, X^S denotes the mutant, dominant X-linked allele for malformed eyes).

Punnett square:

The female will produce gametes RX^s and rX^s, whereas the male would produce two types of gametes viz. RX^S and rY.

RX^s

rX^s

RX^S

RRX^SX^s

(female: red-eyed, malformed eyes)

RrX^sX^s

(female: red-eyed, malformed eyes)

rY

RrX^sY

(male: red-eyed, normal eyes)

rrX^sY

(female: white-eyed, normal eyes)

Therefore, phenotypically all female offspring appear red and malformed eyes, and the male offspring have normal eyes with 1:1::red : white eye color.