Re: How many genes do we differ on?

Date: Fri Feb 16 2001 - 17:04:56 MST

Robin asks,
> Anyone seen the answer to this question: On how many
> genes do two typical humans differ?

I don't have exact numbers to hand, but Futuyama cites large mammals
as being heterozygous (having different genes) at 3.7% of allozymes. That
means 3.7% of the time your two alleles produce proteins of significantly
different motility. Since most variants are rare, two people would differ
at about 7% of loci; with 30,000 loci now estimated for the human population
that's a floor of 2,100 genes. It will be higher as most changes aren't
electrophoretically detectable.

There is a catch with non-protein-coding regulatory regions. We keep finding
more of them, more types of them, they are not readily identified, and they
vary far more than coding regions. There could be a lot of variability
there; I think two unrelated human by that criterion might differ at almost
all loci.

Hal Finney writes:
>Even if we know on how many places people can differ potentially, that
>does not answer Robin's question, which is on how many of those places
>two randomly chosen people would actually differ. No doubt it would
>depend on how closely related the people are, and perhaps on whether
>they are from the same part of the world or the same ethnic group.

Ethnicity and geography turn out to be minor influences on human
coding polymorphism, explaining only about 10% of variation. So, to
first approximations, you can ignore it. However, if those regulatory
region polymorphisms turn out to be important, then that will change;
sharing an entire gene will become rare unless you are related to
the person.

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