In fruit flies, bar eye is inherited by a dominant X-linked allele (B for bar). If a heterozygous bar-eyed female is mated to a non-bar-eyed male, what will be the expected ratio of phenotype given four offspring?
A) two bar-eyed females, two bar-eyed males
B) one bar-eyed and one non-bar-eyed female, one bar-eyed and one non-bar-eyed male
C) three bar-eyed females and one non-bar-eyed male
D) bar-eyed females only
E) non-bar-eyed males only

Question

Quizplus · Accepted Answer

The heterozygous bar-eyed female would have one X chromosome with the dominant B allele and one X chromosome with the non-bar-eyed allele. The non-bar-eyed male would only have non-bar-eyed alleles. The expected ratio of phenotypes would be one bar-eyed female (with the dominant B allele on her X chromosome), one non-bar-eyed female (with the non-bar-eyed allele on her X chromosome), one bar-eyed male (with the dominant B allele on his X chromosome), and one non-bar-eyed male (with the non-bar-eyed allele on his X chromosome). Therefore, choice B matches this expected ratio.

In Fruit Flies, Bar Eye Is Inherited by a Dominant