Question

When a white eye Drosophila male$\left(X^{r}Y\right)$ is crossed to a red eye female $\left(X^R{X}^R\right)$, in the $F_2$ generation all the females are red eyed and $50\%$ males are white eyed. In a criss cross test, when a white eyed female$\left(X^r{X}^r\right)$ is crossed to a red eye male$\left(X^{R}Y\right)$, the $F_1$ generation off spring had white eyed males while the female offspring had red eyes. Instead of crossing of a white eyed female $\left(X^r{X}^r\right)$ to a red eyed male $\left(X^{R}Y\right)$, white eye female $\left(X^r{X}^r\right)$ to white eye male $\left(X^{r}Y\right)$ is crossed, the $F_1$ generation will have the following phenotypes and genotype.

• A. All females have white eye $(X^r{X}^r,X^r{X}^r)$ and all males have red eye $(X^{r}Y,X^{r}Y)$
• B. All females have white eye $(X^r{X}^r,X^r{X}^r)$ and $50\%$ males have red eye $(X^{R}Y,X^{r}Y)$
• C. $50\%$ females have white eye $(X^r{X}^r,X^R{X}^r)$ and all males have white eye $(X^{r}Y,X^{r}Y)$
• D. All females have white eye $(X^r{Y}^r,X^r{X}^r)$ and all males have white eye $(X^{r}Y,X^{r}Y)$

Answer 1

The correct option is D All females have white eye $(X^r{Y}^r,X^r{X}^r)$ and all males have white eye $(X^{r}Y,X^{r}Y)$

In the given example, red eye is dominant over white eye. When a white eye Drosophila female (X${}^r$X${}^r$) is crossed to a white eye male (X${}^r$Y), in the F${}_1$ generation all females have white eye with genotype X${}^r$X${}^r$ as each parent will give X${}^r$ gene to the daughter. All the males in F${}_1$ generation will have white eye too with the genotype X${}^r$Y as he will receive X${}^r$ gene from mother and Y gene from the father.

Thus, the correct answer is option D.