Kneecoal

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Mar 2, 2009
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Question in the genetics section of Cliff's:

Lat A and a represent 2 alleles for one gene and B and b represent two alleles for a second gene. If for a particular individual, A and B were on one chromosome, and a and b are on a second chromosome, then all of the following are true except:

So 2 of the choices are:
- the two genes are linked
- all gametes would either be AB or ab

So the latter is obviously not true, but the first choice - they say in the answers that since they're on the same chromosome, they're technically linked - nothing about whether they're close enough to show linkage.

Am I getting too technical here?
 

bennijai

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May 23, 2006
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Gene A and B are on one chromosome and gene a and b are on the other. Hence the reason why the genes are linked. Basically gene 'A' and 'B' will always show up together, the same for gene 'a' and 'b'.
 
Jun 14, 2009
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i know, but i'm thinking more in terms of % recombination - that was where i tripped up
Linkage only deals with the attribute of being on the same chromosome. Even if they're so far apart that they show almost independent segregation, their presence together is considered a linkage. If you want to argue that genes that recombine are not linked, you'd have to consider every pair of genes in existence unlinked :(
 
May 15, 2009
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Question in the genetics section of Cliff's:

Lat A and a represent 2 alleles for one gene and B and b represent two alleles for a second gene. If for a particular individual, A and B were on one chromosome, and a and b are on a second chromosome, then all of the following are true except:

So 2 of the choices are:
- the two genes are linked
- all gametes would either be AB or ab

So the latter is obviously not true, but the first choice - they say in the answers that since they're on the same chromosome, they're technically linked - nothing about whether they're close enough to show linkage.

Am I getting too technical here?
Two genes on the same chromosome are always considered to be linked. However, when they are far apart, their recombination frequency starts approaching 50%, causing the two genes to behave as if they were unlinked. This makes it difficult for us to figure out whether the genes are really linked or not, if we have no previous knowledge regarding the loci of the two genes. So, the analysis of linkage becomes more difficult when two genes on the same chromosome are far apart, because of how they behave, but that doesn't change the fact that they're linked.