Re: How can chromosome numbers change?

On Feb 18, 12:14 pm, "Erland Gadde" <erl...@xxxxxxxxxxxx> wrote:
Human beings have 46 chromosomes (23 pairs), while other apes,
including chimpanzees, have 48 (24 pairs). This means that at some
time since the split of the ancestral lineage connecting humans and
chimpanzees, a human ancestor lost a chromosomal pair, problably by
two pairs merging into one.

But how can that have occurred? If a child of parents with 48
chromosomes by some reason got 46 chromosomes, how could that
individual mate with other specimen with 48 chromosomes? Or should we
assume that that individual had a sibling who also had 46 chromosomes,
and that those siblings mated and that all humankind descends from
those two siblings? Or did the bond where two chromosome pairs were
merged to one evolve during the generations, so that it was quite
loose from the beginning, so that originally it could weaken and split
the cromosomes and than tying it up again, forward and back in the
cells of an individual, allowing those individuals to sometimes mate
with individuals with 48 chromosomes, when their gamete chromosomes
were temporarilly untied, but that the bond evolved and became
stronger during the generations, until it it became unbreakable?

I would be interested in learing more about this...

Regrads,

Erland Gadde

The chromosomes 2q and 2p (which appear in apes) is fused in the human
lineage into a single chromosome (chromosome 2). (You can see this in
the illustration here: http://www.gate.net/~rwms/hum_ape_chrom.html)
They fused at the telomeres. (So the human lineage actually has a
telomere in the middle of chromosome 2 and two centromeres.) There
are species alive today who have variable numbers of chromosomes, and
it doesn't seem to affect an organisms ability to interbreed with
another organism with a different number of chromosomes. My guess is
that when a fused-chromosome organism mates with an unfused-chromosome
organism, there might be a bias towards breaking the fused chromosome
into two or fusing the two chromosomes into one. If the bias remains
constant, it would eventually lead to a species with a chromosomes
that are universally fused or split. I believe that neanderthals had
the same fused chromosome structure as humans, which tells us the
chromosome fusion happened a while ago in the human lineage.

There's some more information here: http://www.gate.net/~rwms/hum_ape_chrom.html


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