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Mendelian Genetics Problem

  1. Jan 21, 2013 #1
    1. The problem statement, all variables and given/known data
    Mendel's explanation for the monohybrid crosses predicts that the phenotypic 3:1 ratio in the F2 can be explained by an underlying genotypic ratio of 1:2:1 (eg. 1PP:2Pp:1pp). How could you test to see if the purple flowered F2 were really in the ratio of 1PP:2Pp?

    2. Relevant equations

    3. The attempt at a solution

    Starting from the beginning, there would have to be 2 homozygous parents, one with the recessive trait (white flowers, p) and the other with the dominant trait (Purple flowers, P).

    P: PP x pp

    F1 : Pp --> Self breeding the F1 will always give an F2 with a 1PP:2Pp:1pp ratio (when set up in the punnet square). Both Pp's will have purple flowers, PP will also have purple flowers, and pp will have white flowers, ie a 3:1 ratio. So to test if the F2 was really in a 1PP:2Pp ratio you could do a test cross. If you crossed it with a homozygous recessive plant, you would get a 1Pp:1pp ratio out. Would this be enough to prove it? Is it only possible to output a 1Pp:1pp ratio if the purple one was in a 1PP:2Pp ratio? how does it prove it?

    Does my reasoning seem correct, or am I just going around in circles with my explanation?
  2. jcsd
  3. Jan 22, 2013 #2


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    Staff: Mentor

    Just for the Pp parents. Don't forget the PP part, it will change the ratio.
    You can use this to test the fraction of Pp in the purple flowers, right.

    Gene tests would be easier, of course ;).
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