Why are there 23 pairs of chromosomes?

Helene Klapper hk-miami at ix.netcom.com
Fri Jul 7 18:01:28 EST 1995


In <3tk22o$d6e at news.ox.ac.uk> Netscape User
<netuser at eromanga.pmb.ox.ac.uk> writes: 
>
>Hi,
>   Why are there only 23 pairs of chromosomes in human while simpler
creatures may 
>have many more chromosomes?  What are the mechanisms that decide the
number of 
>chromosomes in a creature?
>   All plausible suggestions will be much appreciated.
>
>best regards - teck sin
>
The size of the genome is probably more relevant than the number of
chromosomes.  Some organisms may have many, but they may be very small
(such as avian microchromosomes). Certainly over time, evolution has
contributed to the breaks of large xms into smaller ones, and the
joining of smaller ones into larger ones.  So, you could say that the
xm number is always changing  ( over millions of years, anyway). 
Besides, there is so much junk dna in the xms...the number of xms or
size of the genome is not really indicative of the number of genes
present...and the genes being present doesn't mean that they are
active.  I guess what I'm saying is that the number 23 is really
meaningless - we could have many more or many less, and still have the
same number of genes.



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