How do I solve this using the 5 steps of punnet squares?

Question

In cats, fur color is X-linked. Black fur is dominant to yellow fur; he heterozygote produces tortoiseshell fur.

a. Cross a tortoise shell female with a yellow male.

b. Cross a black male with a yellow female.

Please use the 5 steps of the Punnett Square.

Answer 1

Here is my answer! You should be able to solve the next two problems if you understand what I did. If you struggle with them, please send me a message or reply to this thread and I'd be happy to help!

Answer 2

We are told that black fur is dominant to yellow, but what is omitted -- and is very important -- is that only females can be tortoiseshell. So, let's use some symbols to define our genotypes, and then we can start making our square; X and Y are sex chromosomes, and the superscript denotes which fur allele is present, B = black and Y - yellow:

X^BX^B = black female X^YX^Y = yellow female X^BX^Y = tortoiseshell female

X^BY = black male X^YY = yellow male

Because the fur coat color is on the X chromosome, they will always be inherited together. Also note that the Y chromosome has "no allele" associated with it, because there are no genes on there that we care about for this problem. Now, it's just the matter of using the appropriate genotypes when setting up the square.

(a) X^BX^Y x X^YY = Females: 1/2 will be X^BX^Y (torties) and 1/2 will be X^YX^Y (yellow)

= Males: 1/2 will be X^BY (black) and 1/2 will be X^YY (yellow)

You would solve (b) the same way, just make sure you use the correct genotypes for your gametes, or you will be very sad!