Re: Human Genome May be Longer than Expected
Tue, 3 Aug 1999 00:24:59 EDT

In a message dated 8/2/99 7:35:56 PM Mountain Daylight Time, writes:

> My books and articles are in storage for the next month so I can't look
> this up again. But I believe that this was based on a DNA hybridization
> technique in which a strand of human and a strand of chimp DNA were allowed
> to combine. One of the strands was normal the other was the anti-sense
> copy. The excess and shortages were calculable from this. And this
> technique allowed them to determine the percentage of identity. Does
> anyone else have a more firm piece of information?

The method is based on the temperature needed to separate the sense and
antisense strands from each other; this is known as the melting temperature.
This temperature is directly related to how strongly the sense and antisense
strands bind to one another, which in turn is directly related to how similar
the sequences of the sense and antisense strands are to one another. If the
sequences are identical (from the same species) then the melting temperature
is at its maximum; the more dissimilar the sequences are, the lower the
melting temperature. Chimp DNA is so similar to human DNA that a human sense
and a chimp antisense strand melt at a temperture that is only 2% lower than
that of human/human or chimp/chimp DNA. However, this method can only give
you a qualitative determination for DNA as a whole; it cannot give you
quantitative determinations of each gene. Fortunately, sequencing of human
and chimp genes have verified rather than refuted this 98% value (so far).

Kevin L. O'Brien