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identical twins

Brian Foley brianf at med.uvm.edu
Tue Jul 9 18:01:04 EST 1996

Brent Gilbert (bg005d at uhura.cc.rochester.edu) wrote:
: In <4rccbo$1hp at news2.ios.com> knanette at village.ios.com (Nanette Knaster) writes:

: >If identical twins marry identical twins, are the offspring of each
: >marriage (cousins) considered to be siblings genetically since both sets
: >of offspring share the same gene pools. 

: Not likely. Remember, almost every cell in the human body, save Erythrocytes
: and sperm/egg cells, have two sets of chromosomes. So, let's say one set of
: twins has the genotype Bb for eye color ( that is, brown eyes, but a carrier
: of the blue eyes trait) and the other twin have the same, the offspring can
: ber either BB, Bb, or bb, hence not identical in this respect.

	The question was not whether the offspring would all be identical,
but if they would be "siblings" in a genetic sense.  Indeed they would
each share the same degree of genetic similarity (50% on average)
as normal siblings.  I am not sure if there is a strict "genetic definition"
of what siblings are.  While identical twins marrying identical twins may
be rare in humans, the situation ocurs frequently in other species,
such as in hybrid maize.
	So the answer is that the offspring would have the same
genetic similarity as siblings.  ANy child of one couple would have
as much in common genetically with a cild of the same couple (legal
sibling) as they would in common with any child of the second 
couple (legal cousin).

Brian Foley

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