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Drosophila genetics problem

  1. Jun 7, 2010 #1
    Hello,

    I want to study the inheritance of red eyes and white eyes in drosophila.
    I have mated red-eyed females with white eyed males.

    F1: All F1 females were white eyed and all F1 males were red-eyed.
    19 white eyed females and 22 red eyed males.

    I have also crossed the females and males of the F1 generation, but this is not relevant for my question.

    I am trying to draw a pedigree chart for the P generation and their offspring, but there is a small problem. I know that this trait is sex-linked, and that the white eyes allele is recessive. Let R denote the red eyes allele and r the white eyes allele. Here is what I get:
    16m3vrc.jpg
    Please, what is the problem?
     
  2. jcsd
  3. Jun 7, 2010 #2

    Ygggdrasil

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    You are correct, these data are clearly inconsistent with the white eye trait being a sex-linked recessive trait. These data are consistent, however, with a different type of inheritance for the white eye trait. Can you determine what this mode of inheritance is?
     
  4. Jun 7, 2010 #3
    Hmm I don't really see what mode of inheritance it could be... can you give me a hint?
     
  5. Jun 7, 2010 #4

    Ygggdrasil

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    Well, first consider whether it is sex-linked or not. Do the data suggest that it is sex-linked? Once you figure out whether it is sex-linked or autosomal, you can try assuming that it is recessive and see whether the results match, then try assuming its dominant.
     
  6. Jun 7, 2010 #5
    I have tried sex-linked and it didn't work. The data suggests it is sex-linked, and I know that answer is recessive sex-linked. Recessive sex-linked is what I tried and it didnt work. I think I am missing something... please help me

    EDIT: By the way, the method I have tried is assuming the inheritance mode is sex-linked. Maybe I should have put R as an exponent

    EDIT2: After re-reading your post it seems like you've understood my try of the white eye being a sex-linked recessive trait. This is what the data suggests. However, the pedigree does not work, and I thought after reading on wikipedia that it was indeed a sex-linked recessive trait. I am lost
     
    Last edited: Jun 7, 2010
  7. Jun 7, 2010 #6

    Ygggdrasil

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    Assume white eyes are a sex-linked dominant trait. In your red-eyed female x white-eyed male cross, what would you expect?

    Now, the white eyed trait is normally a recessive sex-linked trait. Is this problem from a class or did you actually do this experiment and get this data?
     
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