## How do you know the number of gametes produced from a cross?

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Nivea
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Posts: 4
Joined: Sat Jan 29, 2011 4:46 pm

### How do you know the number of gametes produced from a cross?

I understand that a general formula for
F1 gametes is 2^n,
F2 genotypes is 3^n and
F2 phenotypes would be 2^n,
where n is the number of genes.
However, I am confused how the answers come about, I'm more of a visual learner so I'd benefit more by seeing the different gametes and counting them, math just confuses me.
I was thinking since gametes are haploid then for
a) the potiential gametes would be A and a, which are 2.
Then for b) A,a,B,b which are 4.
And finally c) A,a,B,b,C,c which is 6--but when you do the formula for this one, you get 8? (2^3 = 8 )
I think I am misunderstanding the concept. Would someone please explain this, I have a test coming up so I would really appreciate it, thank you so much in advance!

How many different kinds of F1 gametes, F2 genotypes, and F2 phenotypes would be expected from the following crosses:
(a) AA x aa;
(b) AA BB x aa bb;
(c) AA BB CC x aa bb cc?

JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm
You MUST always have all the genes in your gamete, so for two genes you can have AB, Ab, aB or ab; for 3 genes it is ABC, ABc, AbC, aBC, abC, aBc, Abc or abc, that is 8 possibilities
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

Nivea
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Posts: 4
Joined: Sat Jan 29, 2011 4:46 pm
Ah that makes a lot more sense, thank you!

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