🚀 go-pugleaf

Alexander Kennedy (akennedy@gpu.srv.ualberta.ca) wrote:
: : are probably slight variations of each other.  Crossing over has nothing
: : to do with alleles.  Just think of it this way.  If genes did not have

: 	Wow... this seems to me to be wrong, in at least some sense... 
: crossing over effects the combination of alleles in an operon, and thus 
: the expression of that trait... also, although I'm not sure about this 
: (genetics is not my discipline *^_^*) but can't crossing over occur even 
: in the middle of a gene?  if there was only a difference of a single 
: point mutation in the alleles, I concede this would only yield a change 
: in the allele on each strand, but if there were multiple point mutations, 
: deletions or additions, or other multiple-base-pair mutations, wouldn't 
: the nature of each allele be drastically changed?


You are right -- there are two ways to create new alleles by 
crossing-over between two copies of a locus.  One is the situation
you describe -- if intragenic recombination combines differences
at two different locations within the gene.  The other is if 
the crossing-over is imprecise and one copy is shifted relative
to the other before recombination.  This results in one copy 
growing and the other shrinking.

	ABBBBC
          |||		If pairing occurs here
	 ABBBBC

	ABBBBBC		increased by one B
	 ABBBC		decreased by one B

As shown in the diagram, this is most likely to occur if there is
a repetitive region of the gene, and such regions are not uncommon.

Keith Robison
Harvard University
Department of Cellular and Developmental Biology
Department of Genetics / HHMI

robison@mito.harvard.edu