In a cross between a white-eyed female with two X chromosomes and one Y chromoso
ID: 276990 • Letter: I
Question
In a cross between a white-eyed female with two X chromosomes and one Y chromosome (XwXwY) with a red-eyed male, the majority of the males have white eyes and the majority of the females have red eyes. However, rare red-eyed males and white-eyed females are present as well. What is the most likely chromosomal constitution of the red-eyed males and white-eyed females resulting from this cross?
Notes: Xw is recessive (white) and X+ is dominant (red). The answer is not A.
Also, I am not just looking for the answer but I am also looking for an explanation!
A. X+XwY males and Xw femalesExplanation / Answer
The female Drosophila with white eyes is recessive and the male with red eyes is dominant. The reciprocal cross may produced red eyed males and white eyed females. The female genotype is XwXwY and male genotype X+Y. Now in the reciprocal cross the sexes and phenotypes are interchanged between male and females. Therefore, in this reciprocal cross, Xw gene of female is moved to males and X+ of males is moved to females. As a result the genotypes of red males and white females resulted are XwX+ females (white eyed) and XwY males (red eyed). Option D is correct.