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self-fertilization

Genetics as it applies to evolution, molecular biology, and medical aspects.

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self-fertilization

Postby rleung » Thu Jun 30, 2005 11:12 pm

I don't get how they get the answer to the following question. If anyone could provide any assistance, I would appreciate it so much. Thanks :)

Study the experimental results in a Mendelian cross between a male parent with genotype RrYy and a female parent with RrYy. To further test his hypothesis, Mendel let the F2 progeny from this experiment self-fertilize. Then he examined the phenotypes of the F3 generation.
R=round
r=wrinkled
Y=yellow
y=green

1) Consider the F2 individuals that have one dominant and one recesssive trait (yellow and wrinkled seeds or green and round seeds). When they self-fertilize, what fraction of these individuals will be homozygous for these traits?

A: The book answer says 1/3, but I get 1/2. I counted up 6 offspring in the F2 generation that will be either round and green or wrinkled and yellow (1 RRyy, 2 Rryy, 1 rrYY, 2 rrYy). In the self-fertilizations involving RRyy and rrYY, 100% of the offspring will be homozygous for both these traits, while 25% of the F3 will be homozygous for these traits when you self-fertilize any of the F2 progenies that have the genotype Rryy or rrYy. Therefore, I get 1/2?

2) Consider the F2 individuals that have both dominant traits. When they self-fertilize, what fraction of the progeny will be homozygous for these traits?

A: 1/9, but using my above-menioned logic, I do not get that either.

Thanks so much.

Ryan
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Postby MrMistery » Fri Jul 01, 2005 8:21 pm

I did it too. You seem to be right....
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thanks

Postby rleung » Sat Jul 02, 2005 7:38 pm

Thanks. So for the second part of the question, you do not get the book answer as well? Thanks.

Ryan
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Postby MrMistery » Sat Jul 02, 2005 7:51 pm

At the second one i got 1/16
Strange...
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Postby LrdGeno » Thu Jul 07, 2005 9:33 pm

did the question want the individuals that are homozygous for both traits? I'm not even sure that would have a bearing on the answer becuase i'm kinda confused on how to do punnett squares with more than one characteristic. Just now learning about Mendel.
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Postby LrdGeno » Thu Jul 07, 2005 9:51 pm

having read the tutorials on the forum I figured out how to do it, and I got the same answers you guys did, so perhaps the book was mistyped.
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