I have to make a punet square...?

Question

I need to make a punet square for something. This is what my teacher said after she said punet square. Make a dihibrate cross to illustrate the Principal of Independant Assortment. One parent with Rr and Dd crosses over with another who has exactly the same Rr Dd. I dont get what I'm supposeed to do. I also need to write the genotypic ratio and the phenotypic ratio. It's due on Monday. Tnks.

Answer 1

Actually, it is possible to create a punnet square with a dihybrid cross. What you need to do is find all possible combinations of Rr and Dd. These are RD, Rd, rD, and rd. You will have a 4x4 square.

RD Rd rD rd
RD
Rd
rD
rd

This is how to set up your Punnet square. All you have to do now is cross them.

RD Rd rD rd
RD RRDD RRDd RrDD RrDd
Rd RRDd RRdd RrDd Rrdd
rD RrDD RrDd rrDD rrDd
rd RrDd Rrdd rrDd rrdd

The genotypic ratio corresponds to the actual letters. The genotypic ratio is 1:2:1:2:4:2:1:2:1

This is because there is
1 RRDD
2 RRDd
1 RRdd
2 RrDD
4 RrDd
2 Rrdd
1 rrDD
2 rrDd
1 rrdd

The phenotype ratio corresponds to what they will look like. All RR and Rr are considered the same phenotype, as well as DD and Dd. The phenotype ratio is 9:3:3:1 because there will be 9 possible combinations that will have both dominant genes. There will be three with only the dominant R gene, and three with only the dominant D gene. There is only one possibility with both recessive genes.

I hope that this helps.

Answer 2

You cant cross Rr and Dd. It has to be Rr, Rr and it would come to 25% 1/4 RR Homozygous Dominant, 25% 1/4 rr Homozygous recessive, and 50% 2/4 Rr Heterozygous dominant. If its Dd Dd, it will be the same but plug in the new letters.