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Homework Help: Question about biology - gene mapping

  1. Aug 2, 2015 #1
    1. The problem statement, all variables and given/known data
    Screen Shot 2015-08-02 at 8.17.22 PM.png

    2. Relevant equations
    RF = (#Recombinants)/(Total offspring) x 100

    3. The attempt at a solution
    How do I know that b is unlinked? I know that unlinked genes have a recombination frequency of 50% or higher, but how do I calculate RF for the genes here?
  2. jcsd
  3. Aug 3, 2015 #2


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    Homework Helper
    Gold Member

    Practiced geneticists and maybe you by the end of these exercises or others can just look at these numbers and say ah yes this and that are linked in this order, but we have to reason it out bit by bit, remembering what linkage means.

    To start you off, I would say e.g.the female is heterozygous so has genotype Aa so should have 50% A and 50% a progeny.
    But don't rely on it, count them, in fact I find 500/1000 have phenotype + and same number are a.
    Phenotype + is genotype Aa (AA should not be possible), phenotype a genotype aa.
    Is a linked to b?
    If it is unlinked, 50% of the + that have A should have B and be + for the b phenotype, a and b inherited independently.
    If it is closely linked then either 100% or 0% of the a should be + for b.
    I counted up just the + for a and found 254/500 of the +a were +b.
    So loci a and b appear essentially unlinked.
    You should also look at those that were a. Presumed genotypically aa.
    So do all the combinations like that, That should give you the linkages or not, at least for the autosomals
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