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Need Some serious help on a genetic problem

  1. Jun 9, 2004 #1
    The question is

    You have crossed two Drosophila individuals that have long wings and red eyes they wild-type phenotype. In the progeney, the mutant phenotypes called curved wings and lozenge eyes appear as follows:

    Females
    600 long-wing, red eyes
    300 curved wing, red eyes

    Males:
    300 long wings, red eyes
    300 long wings, lozenge eyes
    100 curved wings, red eyes
    100 curved wings, lozenge eyes

    What is the genotype of the female parent?
    what is the genotype of the male parent?

    What i used for my notation:
    L= long wings
    l=curved wings
    R= red eyes
    r=lozenge eyes

    I already know that genotype for the wings its Ll for both parents due to the 3:1 ratio. My problem is how do i do the eyes. This problem was on my last test. And i got the eyes wrong because, the eyes are sex linked. How do i detrmine if it is sex linked or not. And after i find if its sex linked, where do i go from there.

    I really need hlep on this problem. I do not know how to do genetics problem involving sex linked traits. Any one that knows anything about this topic help me out. I would really appreciate it.

    Thanks
     
  2. jcsd
  3. Jun 9, 2004 #2

    iansmith

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    The clues that is sex link, it that the r phenotype is absent from the females and 50% of the males have the r phenotype.

    When it is sex link, the female has to have both recessive allelle t have the r phenotype whereas the male only has one copy of the gene. The gene is on the X chromosome.

    The sex-link square would be as follow for F1

    PHP:
    F1
        XR      Xr
    XR XRXR  XRXr
    Y   XRY    XrY
    In your problem the square would be as follow

    PHP:
    F1
          XRL       XRl       XrL       Xrl
    XRL XRLXRL   XRlXRL   XrLXRL   XrlXRL
    XRl  XRLXRl   XRlXRl    XrLXRl     XrlXRl
    YL  XRLYL     XRlYL     XrLYL     XrlYL
    Yl   XRY       XrYl        XrLYl      XrlYl
     
    Last edited: Jun 9, 2004
  4. Jun 9, 2004 #3
    One last question, That means that the famale has both the R, r phenotype right. One is on one x chromosome and the other is on the other. But how did you detrmine that the male has A R allele, and not a r. Is that because 50% of the males had red eyes.
     
  5. Jun 9, 2004 #4

    iansmith

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    Staff Emeritus
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    it is your stated phenotype was red eye and it is a wild type. A wild type phenotype is the major phenotype in a given population. Therefore it is dominant. You also see that the male carry the R genotype because no female had the lozenge eye phenotype. If a the male would of carry the r genotype and so did the female, 1/8 of the female would have the lozenge phenotype.
     
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