## KrystaRenee Analyze the results of a cross between two organisms that are both heterozygous for two different genes (AaBb). Use a Punnett square to evaluate the possible genotypes. (1) List the 16 genotypes from your Punnett Square in the answer space. (2) Determine how many phenotypes can be produced in the offspring. (3) Determine the probability of producing offspring with the aabb genotype. one year ago one year ago

1. blues

OK, it would be very helpful if you told us what aspect of the prob you would like help with. That way we don't have to work through all the parts you already know. The first thing you want to do is set up your Punnett Square. There are two different genes and I assume the genes are on different chromosomes, so they sort independently during gamete formation. So you have a dihybrid cross. Are you already cool with the simpler monohybrid cross, where there is just one gene involved?

2. KrystaRenee

I need help with the whole thing, that's why I posted the whole thing. I'm not good with any of this. I have no clue what I'm even supposed to be doing.

3. blues

Cool, we can fix that. So a Punnet Square is a tool that shows the different combinations of the parents' alleles that the offspring can get. If you look at the parents' genotype, the chromosomes with the A gene and the chromosomes with the B gene sort independently of each other. That means that when offspring are formed, they can get one of each A/a or B/b chromosome from each parent. Is that much clear?

4. KrystaRenee

Yes lol.

5. blues

OK, so the first step in setting up a Punnett Square is list the possible combinations you can have. It says the parent is heterozygous for both genes, so AaBb. The big A allele can pair with either the B or b, so two of your combinations are AB and Ab. Similarly, the little a allele can pair with either the B or b. So the two possibilities from that are aB and ab. So overall you have four possible allele combinations that the parent can pass on to its offspring: AB, Ab, aB and ab. Cool with that?

6. KrystaRenee

Seems so complicated lol but yes I understand so far.

7. blues

OK, it will become clearer in this step, when you set up your Punnett Square. What you need is a row and a column for each parent. In this case, it tells you that both parents are heterozygotes AaBb, so each parent will have the same combinations. You put one parent's combinations across the top, the other's on the side. It looks like this: |dw:1358394360603:dw| Would you like to take a stab at filling in the square?

8. blues

So the first line filled in looks like this: |dw:1358394891089:dw| The genotypes in the squares are the possible genotypes of the offspring. For example, the leftmost box has a dominant A allele from both parents, so two dominant A alleles. And dominant B alleles from both parents, so two dominant B alleles. AABB. Same explanation for the genotypes in the rest of the boxes.

9. KrystaRenee

So it's different in each square?

The genotypes won't be different in EVERY square. Some will come out the same. And that's okay. All we need to do is fill in every square.

11. KrystaRenee

Ok. Well could you help me fill them out further? I really need to get this done. I'm already behind..

Okay. This Punnett Square has two parents. The first parent's genotypes are on TOP. The second parent's genotypes are on the LEFT side. Take a look at the ones that blues already filled out. The VERY FIRST box, for instance, has the genotype (A A B B). How did he figure that out? What he did was he took the A from the first parent (TOP side) and put it together with the A from the second parent (LEFT side). They both happen to be Capital A's. And then he took the B from the first parent (TOP side), and put it together with the B from the second parent (LEFT side). They were both Capital B's. What he got, in the end, was (A A B B). And you see, that's the very first square. The next that he filled out was (A A B b). And he did that, using the same method.

|dw:1358476429108:dw| Here's the Punnett Square that blues started making. I drew in some lines, for the FIRST square, to show you where the letters came from.

14. KrystaRenee

Ok, I see for that one now. So for the next square would it be AABb? Or AAbb?

The one underneath (A A B B) ? It would be (A A B b).

16. KrystaRenee

Yes. Ok, so I was right lol. So is the question above asking me to fill all of them out and then list them?

Yes. There are 16 squares, in all. The problem asks you to fill them all out, and list all 16 genotypes.

18. KrystaRenee

You don't mind helping me figure them out them? I think the next square is AAbb?

Underneath (A A B b) ? Yes, it would be (A A b b).

What you could do is copy the Punnett square that blues made, and fill the rest of the boxes in. And then you can post that, and I'll check it for you.

21. KrystaRenee

Yes, ok. Sounds good. I will do that.

22. KrystaRenee

|dw:1358477189813:dw| I think I messed some up.