Normal fruit flies have red eyes.Flies with mutations that block the function of the X-linked white gene have white eyes.The wild-type allele is completely dominant to mutant alleles.A white-eyed female fruit fly is mated to a red-eyed male.One of their hundreds of female progeny is white-eyed.What is the likely karyotype of this white-eyed daughter?
A)XX
B)XXY
C)XO
D)XXX
E)XYY

Question

Normal fruit flies have red eyes.Flies with mutations that block the function of the X-linked white gene have white eyes.The wild-type allele is completely dominant to mutant alleles.A white-eyed female fruit fly is mated to a red-eyed male.One of their hundreds of female progeny is white-eyed.What is the likely karyotype of this white-eyed daughter?
A)XX
B)XXY
C)XO
D)XXX
E)XYY

Quizplus · Accepted Answer

The white-eyed daughter likely has an XXY karyotype. This is because the white gene is X-linked, and for a female to express the white-eyed phenotype, she must have two copies of the mutant allele. Since her father has red eyes and thus a normal X chromosome, the only way for the daughter to have white eyes is if she inherited an extra X chromosome carrying the mutant allele from her mother, in addition to the normal X from her father, resulting in an XXY karyotype.

Normal Fruit Flies Have Red Eyes