Question

1. in fruit flies, eye color is a sex - linked trait. red is dominant to white.

a. what are the sexes and eye colors of flies with the following genotypes?

	sex	phenotype
$x^{r}x^{r}$	female	red
$x^{r}x^{r}$	female	red
$x^{r}y$	male	red
$x^{r}y$	male	white

b. what are the genotypes of these flies?
white - eyed, male:
white - eyed, female:
red - eyed, female (heterozygous):
red - eyed, male:

Explanation:

Step1: Analyze white - eyed male

In fruit flies, eye color is sex - linked (X - linked). For a male (XY), to have white eyes, since the Y chromosome doesn't carry the eye - color allele, the X chromosome must carry the recessive allele for white eyes. So the genotype is $X^{r}Y$.

Step2: Analyze white - eyed female

A female has two X chromosomes. For a female to have white eyes (a recessive trait), both X chromosomes must carry the recessive allele. So the genotype is $X^{r}X^{r}$.

Step3: Analyze red - eyed female (heterozygous)

A heterozygous red - eyed female means she has one dominant (for red) and one recessive (for white) allele on her X chromosomes. So the genotype is $X^{R}X^{r}$.

Step4: Analyze red - eyed male

A male has one X and one Y chromosome. For a male to have red eyes, the X chromosome must carry the dominant allele for red eyes. So the genotype is $X^{R}Y$.

Answer:

white - eyed, male: $X^{r}Y$
white - eyed, female: $X^{r}X^{r}$
red - eyed, female (heterozygous): $X^{R}X^{r}$
red - eyed, male: $X^{R}Y$