In fruit flies, the brown gene affects eye color and is located on an autosome, while the miniature gene on the X chromosome affects wing size. A cross between true-breeding miniature-winged, red-eyed females and normal-winged, brown-eyed males produces F1 offspring with a phenotypic ratio of 3 brown-eyed to 1 red-eyed in the F2 generation. The predicted total phenotype counts are 4418 normal wings with red eyes, 4330 miniature wings with brown eyes, 610 normal wings with brown eyes, and 590 miniature wings with red eyes.

1. In fruit flies, the brown gene, which controls eye color, is located on an autosome. Brown
mutants (bw) have brown eyes, while wild-type flies (bw^+) have red eyes. A gene on the X
chromosome, miniature, controls wing size. Miniature wings are caused by the m allele, which is
recessive to the allele for normal wings (m^+). True-breeding miniature-winged, red-eyed
females are crossed to true-breeding normal-winged, brown-eyed males. Predict the phenotypes
(including their ratios of the F1 flies. If the F1 flies are intercrossed with each other, what
phenotypes will appear in the F2 and in what proportions?
Solution
1.
Phenotype
Normal wings Red Eyes 4418
Miniature wings Brown eyes 4330
Normal wings Brown eyes 610
Miniature wings Red eyes 590
2. The F1 was self-crossed to give rise to the F2 generation. Of these offspring, 3/4 had brown
eyes while 1/4 had Red eyes. Phenotypic ratio is 3:1