Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!milton!wcalvin
From: wcalvin@milton.u.washington.edu (William Calvin)
Newsgroups: sci.bio
Subject: Re: Man vs Woman vs Chimp DNA Percentages
Message-ID: <7713@milton.u.washington.edu>
Date: 18 Sep 90 01:01:31 GMT
References: <1803@anaxagoras.ils.nwu.edu> <68103@lll-winken.LLNL.GOV>
Organization: University of Washington, Seattle
Lines: 23

I agree that, at first blush, you'd think that human males and females
ought to differ by one part in 46, call it 2 percent.  But you've got
to remember all that duplication:  85% of all genes in your average
person are homozygous (you have a duplicate copy on the other
chromosome).  Males have a Y chromosome that females lack, but it
only have about two genes on it.  Males lack a duplicate X chromosome
(one reason why there are sex linked diseases like color blindness). 
So females have an extra 15% versatility in backup copies that might
work better (slightly different version number, i.e., allele) on one
chromosome out of 23, and they lack two Y-chromosome genes.  That
makes for a lot less than one percent DNA difference between males
and females.
	The big question is:  Which 1-2 percent of the genome is
causing an ape embyro to develop a chimp brain versus a four-fold
larger human brain?  And modify the brain specializations, such as
the lateralization to left brain of serial-order abilities such as
show up affecting handedness and language abilities?


  William H. Calvin, University of Washington NJ-15, Seattle WA 98195 USA
  wcalvin@u.washington.edu         Favorite books on brains and evolution
  (probably because I wrote them myself):  _The Cerebral Symphony_
  (Bantam 1989); _The River that Flows Uphill_ (Sierra Club Books 1987).