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Genetic fun!

Discussion in 'Off Topic [BG]' started by slick519, Mar 3, 2004.

  1. slick519


    Aug 11, 2001
    Salem, Or
    I have a friend..... who is having some trouble on his biology homework, and he asked me to help him.... errr.... yeah

    So anyway, i need to know what happens when two homozygous recessive traits cross. lets say we have black and white rabbits crossing (bb x ww). the resulting phenotype is all black

    what went on? my, err.. friend wants to know

  2. when two rabbits love each other very much....
  3. If you had asked this at the same time last year, I'd have known it. Let me make a square...More than likely, in this case, the rabbits would be grey, :)
  4. Mike Money

    Mike Money In Memoriam

    Mar 18, 2003
    Bakersfield California
    Avatar Speakers Endorsing Hooligan

  5. this is what the square would look like. i just remembered doing this in science today,

    B= black, capitolized because it is the darker, dominant color
    w= white, lowercase because it is the recessive color

    B w < rabbit would be black

    B w< rabbit would be black

    ^rabbit would be white
    ^ rabbit would be black

    so if the rabbit has 4 babaies, the known case scenario would be 3 black rabbits and i white rabbit, as seen if you go vertically and horizontally.
  6. RicPlaya


    Apr 22, 2003
    The Mitten
    Yeah the dominant thing. Kinda like if your have a kid and your spouse has green eyes but you have brown. The kids will have brown eyes, but sometimes the recessive gene pops up and the kids wil have green eyes, but not likely.
  7. slick519


    Aug 11, 2001
    Salem, Or
    the thing is... both are recessive. is it co-dominance? incomplete dominance? dominatrix?

  8. Scott D

    Scott D

    Apr 21, 2003
    Minneapolis, MN
    It couldn't be black. If it was a punnet square with bb on one side and ww on the other, the resulting phenotype would be 100% grey.
  9. Tsal


    Jan 28, 2000
    Finland, EU
    What happens is Bw, black is the dominant so it shows.

    Should this be Bw ww, then there would be Bw, ww, Bw, ww, or
    Bw BB would be BB wB BB Bw, where all rabbits would be black if black is dominant.To have BB as a second generation, you'd need B on both 1st generation rabbits.

    What could happen, is BB at 3rd generation, Bw x B? -> BB.

    You know, to be exact, if there's only one gene affecting the attribute, the letter comes from the dominant attribute. So it wouldn't be "Bw", but "Bb", B being the black and b being the white.
  10. bassmantele


    Jul 22, 2003
    Boston MA USA
    You're not stating the question properly.

    If you want to know what the explanation for

    Black x White --> all black progeny

    The answer would - most likely - be that both the black and the white rabbit were homozygotes, and black is dominant to white.

    The other - different - part of your question:

    "So anyway, i need to know what happens when two homozygous recessive traits cross."

    is not clear. Coat color is one trait with two phenotypes (in this case). In your example, two homozygotes crossed, producing heterozygous genotypes and expressing the dominant allele (black). To actually cross two traits, you'd be dealing with something like coat color and eye color. Since your cross describes the classic single gene BB x bb --> Bb dominant situation, I assume you really are not interested in "two traits".

    What you have here is a gene for coat color. The gene produces black pigment. Each individual has two copies - alleles - of this gene. Each parent contributes one allele for each gene. Sometimes there is a mutation that knocks out the function of the gene. In this case, the mutant allele is incapable of producing black pigment. What your test cross showed is that you only need one copy - allele - of the functioning gene to produce black fur color. That is the definition of a dominant gene - if you get one black and one white, the black is expressed in the body and the black phenotype is produced. Your test cross revealed that one of the parents had two working alleles - black phenotype - and the other had two mutant non-functioning alleles - white phenotype.

    Yes, I T.A.'d Genetics 201.
  11. slick519


    Aug 11, 2001
    Salem, Or
    well, my bio homework was turned in.... and earlier posts all about that the color black just naturally goes over white.... those were true according to my biology teacher. Even with both being recessive.

    oh well
  12. bassmantele


    Jul 22, 2003
    Boston MA USA

    Something's wrong here. "Just naturally goes over" is not a genetic explanation.

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