From: Ian A. York
Newsgroups: sci.med
Subject: Re: Web site re DNA for public?
Date: 23 Jul 1999 16:54:54 -0400

In article <3798C1D5.9A5D3C06@holdit.com>, Ganaan  <holdit@holdit.com> wrote:
>Hello.  I heard a guest speaker on radio talk show say that the monkey
>had 99% of the same DNA make up as humans.  I felt the speaker was
>quietly but loudly conveying his belief in evolution.  Does anyone know
>if there is a web site where where there are statistics, etc..showing
>other facts?  For example, is a horse's dna 99% the same as humans?  I
>am looking for a site that I can understand.  I am just regular

I bet you misheard a little.  A *chimpanzee* DNA is around 98% identical
with a human.  Of course, chimps are apes, not monkeys.  I don't know if
you breath a sigh of relief at the difference between 99 and 98%, either
("Oh, phew!  I thought you said 10 *million* years!").  Estimates of
similarity between humans and chimps range from 95 - 98.5%.

To put this into some kind of context, the human genome is about 3 x 10^9
base pairs long, so that means that between the average human and the
average chimp there are about 6 x 10^7 differences (60,000,000 different
base pairs).  Those arose over around 8 million years since humans and
chimps diverged from their common ancestor.

Since neither the human nor the chimpanzee genome has been completely
sequenced, this is an estimate rather than an exact number.  It was first
worked out by analyzing the way the DNA paired after being unpaired.
That is, simplifying wildly, if you separate the two strands of DNA, and
then mix two strands, the rate at which they re-bind is related to the
similarity.  I believe the original paper was Science 1976 Nov
19;194(4267):846-8 Thermal stability of human DNA and chimpanzee DNA
heteroduplexes. Deininger PL, Schmid CW.

Although the whole genome hasn't been sequenced, of course many individual
genes have been and they are consistent with this, averaging maybe 95% or
so identical.  (If you don't want to believe the published reports, I've
sequenced a couple of genes from African Green Monkey, and they were 95
and 99.5% identical to the human sequence; they were both genes that tend
to be fairly similar across species, though.)

This has been done for many other species, but offhand I don't know about
horses and humans.  My guess is that you'd be looking at something like
80% identity.   Humans and horses, different though they appear at first
glance, are fundamentally piles of bones wrapped in hairy skin, after all.

I don't know of a web site that covers this.  You can always poke around
PubMed at <http://www.ncbi.nlm.nih.gov/PubMed/medline.html>.

Ian
--
    Ian York   (iayork@panix.com)  <http://www.panix.com/~iayork/>
    "-but as he was a York, I am rather inclined to suppose him a
     very respectable Man." -Jane Austen, The History of England