Question

Eye pigment in a particular strain of fly is determined by two genes. An autosomal gene that controls the color of the pigments in the eye has two alleles: a dominant allele ( R ) that results in red eyes and a recessive allele ( r ) that results in sepia eyes. A sex-linked gene that controls the expression of the colored pigments also has two alleles: a dominant allele ( T ) that allows for expression of the colored pigments and a recessive allele ( t ) that does not allow for expression of the colored pigments. Individuals without a T allele have white eyes regardless of the alleles of other eye-color genes.
Which of the following represents a cross between a white-eyed female and a red-eyed male?


TtXRXR×ttXrY
A

TtXrXr×ttXRY
B

RRXTXT×RrXTY
C

RrXtXt×RrXTY

Answer 1

RrXtXt×RrXTY is representing the cross between the white eyed female and red eyed male.

Option D

Explanation:

The genes that are discussed here both are completely dominant over their recessive alleles. In the autosome, the dominant R gene is responsible for red eye and recessive r gene is responsible for sepia eye. But in allosome, the dominant T gene allows the eye colour to be expressed and the recessive t gene doesn't allow eye colour to be expressed and makes it white.

As the female do have 2 X chromosomes and the female is white eyed, then both the chromosomes of female have t gene.

As the male is red eyed and have one X chromosome, so the male must have atleast one R gene in autosome to make the eye colour red and must have T gene in his X chromosome to make it appear in phenotype.

So the most possible cross that is given here is RrXtXt×RrXTY.