X-linked Inheritance Consider this imaginary animal, the tree rat. They are usua

Question

X-linked Inheritance

Consider this imaginary animal, the tree rat. They are usually black, but sometimes they can be purple. The allele for the purple color is X-linked. You manage to capture two of these animals from the same family, a black female and her purple male offspring.

Next you breed the tree rats to each other (inbreeding is acceptable in this case). What percent of the offspring do you expect to be purple? Are any of them female? Use a Punnett square to show your work. [Use the letters B (black) and b (purple) to represent the alleles.]

Explanation / Answer

The traits for black female are B and X whereas the traits for purple male are b and Y.

B and Y should be on top left and bottom left of the table just like a normal 4x4 Punnet square. There is no space on the left side of the table so I cannot denote. Assume it's b on top left and Y on bottom left.

Cross    BX    x bY

                 b Y

Bb

BY

Xb

YX

In case of offsprings Bb and Yb will show purple color because it has x linked recessive trait. So, percentage of purple offspring is 50%

There are two female offsprings Bb and Xb.

Bb

BY

Xb

YX

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