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## Gene Mapping

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

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### Gene Mapping

I need help with a gene mapping question. How do I determine a percentage of recombinations based on genotypes and map units?

I know how to do three-point mapping, but working backwards is always hard for me. Here's a question I'm having trouble with:

A plant of genotype AB/ab is crossed to a plant ab/ab. If the loci are 10 map units apart, what proportion will be AB/ab?

Basically, I attempt setting up an equation along the lines of .10 = recomb/total, but I'm not sure how to differentiate the recomb number if I'm looking for a specific genotype. Will someone walk me through this? I will be extremely appreciative!
Deinonychus
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Joined: Mon Oct 10, 2005 6:25 pm

### Gene Mapping

The cross your dealing with is a test cross. You have to look at it this way: AB/ab X ab/ab will yield 4 different gametes from the AB/ab parent (AB, Ab, aB, and ab) and only one possible gamete from ab/ab (ab). Therefore, any gamete that isn't AB or ab is only possible via recombination. So, if recombination is 10% (c=0.10) then you know that the recombinant Ab and aB gametes make up 5% each (2*0.05 = 0.10). Now all you have to do is subtract from 100% (or 1) and you get 90% that are parental gametes (1-0.1 = 0.9). Gametes AB and ab each occur 45% (0.45) or together 90% or 0.9 (AB/ab). Hope this answers your question.
jchaky1
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Joined: Tue Oct 11, 2005 7:17 pm

It does. Thanks.
Deinonychus
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Posts: 6
Joined: Mon Oct 10, 2005 6:25 pm

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