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    Genetics -- map units

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    EDIT to the problem below: I just realized that the various numbers of offspring add up to 9900, not 10,000, which is the supposed total. So for problem #2, I randomly added 100 to my recombinant numbers and got the answer, 30.1, which turned out to be correct.

    But the same thing did not work for problem #1. Adding 100 to the recombinant numbers resulted in an answer of 1.2, which is not correct. Nor is the correct answer 1.1, which would make up the distance between 30.1 -- 29 (the distane from sp-cn minus the distance from px-cn.)

    So here are my questions about this new twist: 1) Why would 100 offspring be left out of the various classes of offspring. How is this a reflection of what happens in real life experiments? 2) How do you know where to add the 100 offspring in and where not to? The distance between px-cn didn't need the extra 100. And the distance between sp-cn did. 3) And why isn't any of this working for the distance between px-sp?

    Thank you!!

    Hi. I can't figure out this problem:

    Females heterozygous for the recessive second chromosome mutations pn, px, and sp are mated to a male homozygous for all three mutations. The offspring are:

    px sp cn 1410
    px sp + 3498
    px + cn 1
    px + + 11
    + sp cn 8
    + sp + 0 (none seen)
    + + cn 3483
    + + + 1489
    -----
    10,000 total

    I correctly figured out that the middle gene is px.
    I correctly figured out that the distance between
    px-cn is 20 m.u.

    But I can't seem to figure out 1) the distance between
    px-sp or 2) the distance between sp-cn.

    Here's what I'm doing:

    First, I assigned the following types to the above listed classes, in the order that they are listed above:

    SCO (single crossover)
    P (parental)
    DCO (double crossover)
    SCO
    SCO
    DCO
    P
    SCO

    1) To figure out the RF of px-sp: [(1 + 11 + 8 + 0) / 10,000] x 100 = 0.2 m.u.

    1) To figure out the RF of sp-cn: [(1410 + 11 + 8 + 1489) / 10,000] x 100 = 29.18 m.u.

    But neither one of those answers is correct.

    Can you please explain how to do this problem?

    Thank you.

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    https://brainmass.com/biology/genetics/genetics-map-units-3764

    Solution Preview

    I would expect that this is a typo in the question. You should not have to guess about the "missing" 100 offspring. While a real experiment is not likely to give such a nice, round number as 10000, a (honest) researcher would never add in numbers that were not there. Finally, I think you switched the numbers of px sp cn and px sp +, as well as + + cn and + + +, in the numbers you gave me (at least based on your attempts at the problem).
    <br><br>So, if px sp + is 1410, and + + cn is ...

    $2.19