🚀 go-pugleaf

Ari-Matti Sar�n (saren@operoni.helsinki.fi) wrote:

: Count again. We have two cromosomes each (one from father, one from mother). 
: Each chromosome has (during part of the cell cycle) two chromatids. That makes 
: 4 alleles. From practical point of view we do have two alleles (one in each 
: chromosome), but with point mutation and couple of billion truckloads of (bad) 
: luck, we may talk about 4 different alleles. 

: Yes, I'm nitpicking - no hard feelings, eh? :-)

: Ari-Matti 

Well, even if the universe aligned to create the incredibly unlikely 
events that you describe, it would still not change the fact that a 
normal diploid individual is never expressing more than two alleles of a 
gene at a time. When there are four potential alleles in the situation 
you are talking about, actually NONE of those alleles are being expressed 
since the chromatin is in a highly condensed and untranscribable state 
(there are a small number few genes that might escape this effect because 
they are necessary for mitosis itself so these are the only possible 
candidates for your four allele nitpicking) 
When the daughter cells  get around to a stage when genes are being 
expressed again, they are once agin diploid with only two alleles to 
express. A Downs syndrome individual would have three alleles for certain 
genes since they are triploid for chromosome 21 but the question was 
focusing on the status quo not the exceptions.

Gregory S. Turenchalk