## Genetics Hard problem!

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nnyeon145
Garter
Posts: 1
Joined: Tue Jul 03, 2012 7:02 am

### 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.

Answer is 34 m.u.

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? what does crossover between nonsister chromatids help with figurig out the location of the alleles?
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JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm
sister chromatids are identical, since they are product of DNA replication
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

Cat
King Cobra
Posts: 635
Joined: Thu Feb 14, 2008 7:40 pm

### Re: Genetics Hard problem!

nnyeon145 wrote: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.

Answer is 34 m.u.

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)

Consider heterozygous parent contribution (second parental allele pair is ba):
Parent allele pairs are B+ (black) and ba (white).
Cross-over allele pairs are Ba (white) and b+ (brown).

As you can see, white can be due to parental and cross-over genotypes. Therefore, you need to discard it from calculations. Thus, you are left with black and brown progeny to consider: (34*100)/(34+66) = 34amu.

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