In one set of experiments, Calvin Bridges crossed white-eyed female fruit flies with red-eyed males. Some of the offspring were white-eyed females. These individuals, he demonstrated, had the genotype _____, which occurred because of _____ during meiosis.

Question

Quizplus · Accepted Answer

White eyes are the result of a recessive mutation on the X chromosome in fruit flies, which are typically XX females and XY males. In this cross, the white-eyed female would have been homozygous recessive (XX) and the red-eyed male would have been hemizygous (XY). The fact that white-eyed females were observed means that the X chromosome with the mutation was able to pair with a normal X chromosome during meiosis in the male parent, resulting in an XXY sperm that fertilized an XX egg to produce an XXY zygote. This is an example of nondisjunction, where the homologous chromosomes or sister chromatids fail to separate properly during cell division, resulting in gametes with abnormal chromosome numbers.

In One Set of Experiments, Calvin Bridges Crossed White-Eyed Female