Question

In Drosophila, normal wings (+) are dominant to vestigial wings (vg) and the presence of eyes (+) is dominant to being eyeless (ey). The offspring of a cross between two unknown parents yielded the following results: 299 normal winged, normal eyed flies; 106 normal winged, eyeless flies; 99 vestigial winged, normal eyed flies, and 33 vestigial winged, eyeless flies.
What genotypes did the parent generation most likely possess?

• A. +vg/+ey x +vg/+ey
• B. vgvg,/++ x ++/eyey
• C. ++/++ x vgvg/++
• D. vgvg/eyey x +vg/eyey
• E. +vg/+ey x vgvg/eyey

Answer 1

The correct option is A +vg/+ey x +vg/+ey

The ratio of various phenotypes can be calculated as follows:

Normal winged, normal eyed : 299

Normal winged, eyeless : 106

Vestigial winged, normal eyed : 99

Vestigial winged, eyeless : 33

The ratio is 299: 106: 99: 33 = 9.06: 3.2: 3: 1 = 9:3:3:1

This ratio shows that parents are heterozygous for the dominant traits as this ratio matches the Mendelian dihybrid ratio. Hence the genotypes of parents will be +vg/+ey i.e. normal winged, normal eyed. So, the correct is '+vg/+ey x +vg/+ey'.