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07-02-2012, 11:46 PM   #1
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TBR Genetics :( Hard problem!

Based on the information in Experiment II, estimate the minimum genetic map distance between the two genetic loci. (Note: One genetic map unit (m.u.)
gives a recombinant frequency (RF) of 1 percent.)

I scanned the whole passage in the attachment.

This is what I did:
B+/ba x ba/ba (parental strands)

If there is no crossover, B+/ba (black), ba/ba (white)
If there is one crossover (between the sister chromatids), BA/ba (albino), b+/ba (brown)

So in the crossover, since crossover was done in between the two alleles, 100+34/200= 67amu. (wrong)

The back of the book started doing crossover between non sister chromatids. What about the crossover between sister chromatids? In the genetics chapter, they have an example where they find out the distance between the genes through crossing over between sister chromatids.
Attached Files
 tbr genetics.pdf (110.5 KB, 24 views)

 07-03-2012, 10:32 AM #2 New Member   Status Pre-Medical Join Date: Jan 2012 Posts: 4 Let me see if I can help. F1 gen is B/b; +/a B/b; +/a(Black) x b/b; a/a (white) What we have is : Black offspring (must no be cross over) Brown offspring ( must be cross over) white offspring (mixture cross over/ not crossed) Now if we add up the possibles of crossover, don't forget the whites that exist that are crossover. One will assume here that if 34 brown crossover's happened, then about 34 white crossover's happened. That would mean that 2x 34/2= 34x 100%= 34 units. Don't be too quick in assuming just because they all look the same, they have the same genes. Epistasis means watch out and be careful. hth, Renee
07-03-2012, 12:42 PM   #3
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Join Date: Jun 2010
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Quote:
 Originally Posted by Reneeisnowhere Let me see if I can help. F1 gen is B/b; +/a B/b; +/a(Black) x b/b; a/a (white) What we have is : Black offspring (must no be cross over) Brown offspring ( must be cross over) white offspring (mixture cross over/ not crossed) Now if we add up the possibles of crossover, don't forget the whites that exist that are crossover. One will assume here that if 34 brown crossover's happened, then about 34 white crossover's happened. That would mean that 2x 34/2= 34x 100%= 34 units. Don't be too quick in assuming just because they all look the same, they have the same genes. Epistasis means watch out and be careful. hth, Renee
hi renee,

that helped a lot thanks! but can I ask why you can assume that the white crossover mice have frequency of 34?? Also in crossover, it's the crossing between two sister chromatids of the same homolog right?

 07-03-2012, 05:10 PM #4 New Member   Status Pre-Medical Join Date: Jan 2012 Posts: 4 Remember that to figure out what the map units are, one effectively is figuring out the average distance between the two. It has to be under 50% to be on the same homolog, otherwise it is called something else, (can't remember right now) I do remember that the less total amount of the recombinants that occur, the closer the two genes are together. This makes sense if you think about playing with a pipe cleaner~ the closer the two points that you want to twist, the harder it is to twist. (sorry, my kids have been playing with pipe cleaners lately) Gee, this link might help explain a little bit more http://en.wikipedia.org/wiki/Genetic...tion_frequency Renee
07-03-2012, 09:12 PM   #5
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Join Date: Jun 2010
Posts: 84

Quote:
 Originally Posted by Reneeisnowhere Remember that to figure out what the map units are, one effectively is figuring out the average distance between the two. It has to be under 50% to be on the same homolog, otherwise it is called something else, (can't remember right now) I do remember that the less total amount of the recombinants that occur, the closer the two genes are together. This makes sense if you think about playing with a pipe cleaner~ the closer the two points that you want to twist, the harder it is to twist. (sorry, my kids have been playing with pipe cleaners lately) Gee, this link might help explain a little bit more http://en.wikipedia.org/wiki/Genetic...tion_frequency Renee
Aw lol. your kids are so lucky to have a mom who is so great at genetics! Thanks for the site. will check it out! This whole thing is kind of over my head! Thanks again!

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