Hello to ASAers,
It's a little hard to know where to jump in to this traffic! The
sequence divergence between human and chimp is now estimated at 1.2%. While
this was originally based on hybridization kinetics, more recent data
depends on actual sequencing. A significant recent reference, which
compares 19 million randomly chosen base pairs of chimp to the entire human
genome, is:
Science 2002 Jan 4;295(5552):131-4 Construction and analysis of a
human-chimpanzee comparative clone map. Fujiyama A, Watanabe H, Toyoda A,
Taylor TD, Itoh T, Tsai SF, Park HS, Yaspo ML, Lehrach H, Chen Z, Fu G,
Saitou N, Osoegawa K, de Jong PJ, Suto Y, Hattori M, Sakaki Y.
These authors find overall 98.77% identity. Of course the identity
is even higher in coding regions.
To be accurate, however, the 1.2% difference reflects the degree of
mismatching of bases, and doesn't include insertions and deletions of more
than a few base pairs. My own guess from recent data is that as much as 1%
of the genome may be involved in these insertions and deletions of hundreds
to thousands of base pairs. So perhaps we should be careful about quoting
the 1.2% number as THE answer.
Francis Collins
-----Original Message-----
From: Marcio Pie [mailto:pie@bu.edu]
Sent: Monday, March 25, 2002 3:08 PM
To: Dick Fischer
Cc: asa@calvin.edu
Subject: Re: Brachiators On Our family Tree? (Common ancestry - direct
evidence?)
>
> >Walt Hicks wrote:
> >
> >This 99% has always confused me in that is is a number that has been
> >quoted for many years. Yet, it is my understanding that neither the
> >chimpanzee nor human genome have been mapped to anywhere this degree of
> >completeness. So what does this 99% mean? (I'm not arguing; I just don't
> >understand.)
>
> The two genomes are approximately 99% identical in what has been mapped
thus
> far. That is my understanding.
>
> Another good question for Francis Collins.
I think it has been measured in terms of human-chimp DNA hybridization.
You heat up a sample with human and chimp DNA, and the strands of DNA
separate from one other, forming single-stranded human and chimp DNA. You
cool down the sample and you will have some hybrid human-chimp
double strands. Now you measure how much heat you need to separate the
hybrid DNA. This temperature is proportional to how similar the sequences
are (number of nucleotide mismatches). This tool has been used a lot in
the early days of molecular systematics, when direct sequencing was much
harder.
Marcio
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