Thread: Question on genetics

Hey guys I have a question here that I am totally stumped on. I was wondering if any of you can help. Here it is:

A rough-coated male guinea pig is crossed with a homozygous smooth-coated female (rr). Their offspring are rough-coated and smooth-coated in a 1:1 ratio. Use a Punnett square to calculate the genotype of the male parent.

If anyone can tell me more on this it would be greatly appreciated.

Thanks

Oohh NO!! BIO202 eh? anyways..


I am assuming that by "rr" you mean it is homozygous recessive.

O.K. I'll try to explain it so that you can do it.

Draw a square and the put a cross in it so you have four squares. The male parent is either rr, Rr, or RR. The female is rr (as you said).

At the top of the box put a small r over each square, representing the female (rr). Next put one of the 3 male possibilities on the left side (one in front of each square).

Redo the square 3 times so you have one example of each possibility.

This next step will be hard to explain. Hopefully you already know though.

The top right square you put two letters. From the top row: The farthest right. From the left column: The top letter.

Do this for all the squares. This is an example:
http://www.usd.edu/med/som/genetics/...um/fig1-13.JPG

Having 4 squares means you will come up with 4 genotypes . If two of these are of one phenotype and two are of the other than you have a 1:1 ratio. Which of your possibilities has this ratio?

Once you find which one you look at the male genotype that you put for that one and, vwhala, you have found your male genotype.

HINT: A genotype of RR or Rr are dominant phenotypes. rr will be the only recessive phenotype. You need two dominant and two recessive.

I already know the answer so if you need me to tell you to help it make sense the just ask. You should try it on your own first though.

I apologize if any of this you already know. I just wanted to make sure I covered all the bases.

Good luck.