Re: Australopithecine chromosomes

Todd A. Farmerie (
Sun, 05 Jan 1997 01:08:44 -0500

Timo Niroma wrote:

> One item that has caught little interest is when and why and with
> consequences two chromosomes have merged in Homo, so that we have 23
> pairs, when the chimpanzees have preserved the 24 chromosome pairs.

Have two chromosomes merged in Homo, or has one split in Pan? What do
Gorilla have?

> How
> many chromosomes did the Australopithecines have? Was this mutation the
> key to the great variety of Australopithecines and was it the key leading
> to Homo?

It is not likely. The Przewalski horse and the common horse have
different chromosome numbers, and taxonomists can't even decide if they
are the same or different species (they can interbreed and produce
reproduction-viable progeny). The break/fusion in primates likely
occurred in repetitive sequence. Thus is probably had little or no
effect on gene regulation or reproduction. (Other rearrangements that
are visible in the banding of the chromosomes are likely to have had a
greater effect on the divergence than the break/fusion.)

> I know that nobody knows, but one can always speculate based on the
> changes occurred during the time.

Nobody know, nor will they, but my guess is that the difference is
incidental, and not causative.