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genetics and your mother

Discussion in 'MCAT Discussions' started by duck2005, Apr 18, 2004.

  1. duck2005

    duck2005 Member
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    remember the passage about phenotype being determined by the mother? what did everyone put for these questions-
    1. why does the larvae have brown eyes and then red at adulthood? i put that the pigment k-something is in the oocyte.
    2. what happens when brown males and brown females mate? well the problem is that it wasnt clear whether this was a BB x Bb or Bb x Bb or Bb x BB cross. I assumed it was Bb x Bb...as this created a perfect answer choice. Of course, all larvae are brown initially (since the mom is). If it was Bb x Bb...1/4th will be red in adulthood. If its BB x Bb or Bb x BB, 1/2 will be red in adulthood.
     
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  3. Marvin O'Connor

    Marvin O'Connor Senior Member
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    I can't vouch for their correctness, but I put the same answer on those two questions as you did. Hopefully we were right.
     
  4. ajnak182

    ajnak182 MCATretaker4life
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    I selected the answer with 1/4 as well. I think it's right, because the answer said something along the lines of "1/4 of the offspring could have red eyes."

    AJ
     
  5. 34140

    34140 Senior Member
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    Yeah it said that all would be born with brown eyes,but then 1/4 would or could develop red eyes
     
  6. AHH78

    AHH78 Junior Member

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    All brown-eyed, 1/4 could be red-eyed was the right answer. If BB x Bb or Bb x BB then all would be brown and would not turn red b/c it is a recessive trait. The only way that to get any red eyed (bb) from two brown-eyed adults is if they both are carriers of the recessive allele. Bb x Bb = BB, Bb, Bb, bb would result in 1/4 being red-eyed as adults.
     
  7. duck2005

    duck2005 Member
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    oh. of course. mental lapse there. so yeah. all red->1/4 brown.
     
  8. I think the question was why the red ones turn brown? -- they don't have the B gene ! I thnk :confused:
     
  9. duck2005

    duck2005 Member
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    I think its b/c the larvae have pigments from the mothers egg. when these run out, the larvae (which is an adult now) loses pigment, unless it has the gene. so the larvae run out of mother's pigment and dont produce anymore b/c they lack the B gene. its hard to say which is a better way of answering this question. they lose pigmentation b/c the pigments fr mom run out, but also b/c they cannot produce more (lack B gene). I guess if u think of it one way (as in asking why they LOSE pigmentation) its b/c mom's runs out. if you think of it as asking why they don't have pigmentation (its b/c they dont have the B gene).
     
  10. I thyink you were supposed to assume that the red color was due to the presence of the pigment. The question was "why did the color change." Although it was present in the ovum, it wasn't sufficient. The choice said that it was just present in the ovum - therefore the color was red at first! doesn't go too far into saying that the pigment will get used up - that is an assumption as to why the color was red.
    DUE to the lack of the B gene, it the pigment wasn't produced - hence the brown color.
    darn confusing
     
  11. duck2005

    duck2005 Member
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    it did say the color gets used up. but still, i see that it can be interpretted 2 different ways. colors there = brown larvae. gets used up = red, unless you have the B allele and can produce the pigment urself. so as to why the color changes from red to brown, i can see that either (a) k-pigment from maternal oocyte gets used up and (b) the offspring lacks the B allele BOTH seem right. in fact, it gets used up AND the offspring lacks the B allele.

    just having it get used up isn't enough, as even when the mothers pigments are used up, 1/2 of the offspring from Bb (female) x bb (male) cross retain the brown pigment.

    however, just "not having the B" allele isn't enough. as in the bb (female) x Bb (male) cross, the offsprings lacking the b allele (bb offspring) do not see a pigment change from brown to red. instead, these offspring start out as red.
     

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