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Homework Help: Genetics recombination questions

  1. Mar 17, 2010 #1
    Confused on 2 questions here

    If a recombination frequency between two genes is 1.5%, what is the distance between the genes in map units on the linkage map?

    a. Impossible to determine, because the interference is not known.
    b. 1.5
    c. 3
    d. 0.75

    Recombination frequencies

    a. arise from completely random genetic exchange.
    b. are the same for all genes.
    c. decrease with distance.
    d. are the same for cis and trans heterozygotes.

    I thought it was b for the first part a for the second part and but I'm wrong. Can someone explain?
    Last edited: Mar 17, 2010
  2. jcsd
  3. Mar 17, 2010 #2
    Sorry forgot to add my explanation

    b. Each % frequency of recombination equals one map unit between the genes. So 1.5% recombination frequency = 1.5 map units apart will result in 1.5% recombination

    a. It can't be (b), because genes are all distances apart; it can't be (c), because frequencies increase with increasing distance; it can't be (d), because the distance between genes is the same whether the alleles are cis or trans loci. So I thought it was a.
  4. Mar 18, 2010 #3
    Help help please.
  5. Mar 18, 2010 #4
    I'm not absolutely sure, but I'd probably agree with your answers.
  6. Mar 18, 2010 #5
    I thought I was right but when I entered it into the system I was wrong. I'm sure the first part is right and I thought the second part was right but I guess not.
  7. Mar 18, 2010 #6


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    I would probably agree too. It is a strange way of examining to ask which of four statements is correct. It seems to me though I am a bit rusty, that you have to a little bit psych what some of the questions mean, if it's any consolation.
  8. Mar 19, 2010 #7
    Well that can't be right since it's marked wrong. Anyone think it's c for the second part?
  9. Mar 19, 2010 #8
    Last edited: Mar 19, 2010
  10. Mar 19, 2010 #9


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    I was thinking D and C. D because as the loci become further apart (low recombination values) the probability of a second crossover increases and the recombination value is overestimated. The only value less than 1.5 is 0.75 (D). I don't know what is meant by "interference" in answer A but that could be correct as well.

    Edit. you are right C can't be correct
  11. Mar 19, 2010 #10
    I finally found some material that helped. I got it right and the answer was D. Thanks guys for your help I really appreciate it.
  12. Mar 20, 2010 #11
    I've been talking about question 2.
    For which one is the answer D? What did you arrive at for number 2?
    The link I recommended explicitly states that trans and cis heterozygotes exhibit equal recombination frequencies.
  13. Mar 23, 2010 #12
    D is the answer for the second question. So you were right.
  14. Mar 24, 2010 #13
    My apologies, I lost track of the question! Technically I wasn't right, the textbook was...:grumpy:
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