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Punnet Squares

  1. Sep 22, 2007 #1
    [SOLVED] Punnet Squares

    The allele for dark hair D is dominant over that of red hair d, and the allele for brown eyes B is dominant over that of blue eyes b. A women is red-haired and has blue eyes. Her husband is dark-haired and has brown eyes.
    a) What are the possible genotypes for the woman?
    b) What are the possible genotypes for the man?
    c) There are 4 possible ways to match the genotypes of these two individuals. In each of the 4 cases, draw a punnet square give all the possible genotypes for their offspring.

    So I know that the woman must have alleles: dd and bb
    the man must have alleles: DD or Dd and BB or Bb
    the 4 ways to match the genotypes are:
    dd,bb x DD,BB
    dd,bb x DD,Bb
    dd,bb x Dd,BB
    dd,bb x Dd,Bd

    For the match in bold writing, i'm not sure how to draw the punnet square.
     
  2. jcsd
  3. Sep 22, 2007 #2

    Moonbear

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    How did you draw them for the other 3 matches? The concept is identical. I think I'll be able to see where you're running into trouble (and therefore follow up with the help you need) if you just show how you set up the Punnett square for either the second or third combinations in your list (skip the first one for now, I won't be able to tell as much from you showing that, unless you just want the practice to show me all of them).
     
  4. Sep 22, 2007 #3
    for the second one:
    dd,bb x DD,BD:
    DB Db
    -------------------------------------------------------
    db DdBb Ddbb
    -------------------------------------------------------
    db DdBb Ddbb

    For the fourth one:
    dd,bb x Dd,Bb, i'm just confused because for the paternal alleles, Dd,Bb, there are many combinations: DB, dB, Db, and db, wheras for the other three punnet squares there were only 2 combinations? Oh I think its just because i was only writing two before when there are actually four options for all of them (some just repeat so I was leaving them out).

    Thanks for making me realize i was doing it wrong!!
     
  5. Sep 26, 2007 #4

    Moonbear

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    Exactly! That's why I wanted to see how you were writing them out, because it would tell me if you were missing a more general concept, or just getting hung up on the last one.

    It's much better when you see it for yourself...now I'm willing to bet you'll never make that mistake again. :smile:
     
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