Quantifying genetic commonality

Joe Felsenstein joe at evolution.genetics.washington.edu
Wed Feb 21 13:51:11 EST 2001

In article <96umk4$sfo$1 at mercury.hgmp.mrc.ac.uk>,
Julian Assange  <proff at iq.org> wrote:
>Nancy Bennett <nancyb at ignet.com> writes:
>> My question is -- can anybody even wildly estimate the degree to which any
>> two randomly chosen humans (or let's make it easier and say any two randomly
>> chosen Europeans) are, in fact, genetically similar?  I recently read on the
>> Human Genome Project web site that humans may have as few as "one gene in
>> 500" that differs between individuals.  This would suggest that, on average,
>> the genes at 99.8% of all loci are identical.  Is this an accurate
>> estimate??
>Yes, depending on what you mean by `gene' and `differ'. But it rarely
>makes sense to talk about this data in absolute terms. You may have 19/20
>positions correct for the state lottery, yet this does not mean you
>have won 19/20ths of the lottery.

I disagree.

I don't think these figures are accurate.  The usual figure for
the degree of difference between the DNA sequence of different
individuals (let's be more precise -- between haploid genomes such as
the sequences of two gametes) is 1 in 1000 bases (sometimes this
is given as 1 in 500, it varies a bit).  But note that is bases, not
genes.  Genes are not 1 base long.

Two (haploid) human genomes are about 99.8% similar, counting bases.
They do not have 99.8% of all loci identical.

Joe Felsenstein         joe at genetics.washington.edu
 Dept. of Genetics, Univ. of Washington, Box 357360, Seattle, WA 98195-7360 USA


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