Human Chromosomal Number

[colinha]

It has recently been found that the reason that humans have two less chromosomes than other great apes is due to a merging of two chromosomes into one in the past. So we have 23 pairs not 24 as in chimps.
I assume that it would be impossible for us to mate with great apes because the cellular mechanisms would not now be compatible because of this.
My question is as follows.
Since this merged chromosome probably appeared as a mutation in one individual, how did that individual manage to mate and pass on the new 23 chromosome pattern when all possible mates had a 24 chromosomal pattern?
Or am I misunderstanding?

[d9f1c7]

You are misinderstanding. Although most have the standard XX/XY 23 pairs. There are literally millions of anomolies on the gene pool. There is the XYY man for example and The XXY woman, not mention the chromsome orphans etc. O level biology should bring you up to speed.

[jake-the-peg]

I think it's not that simple - for example Downs syndrome is cause by part of an extra chromosome

[colinha]

I believe that most people with chromosomal abnormalities (such as Downs ) are infertile?

[Nibble]

Not true, females with Down's Syndrome are fertile, see below

http://www.ds-health.com/faq.htm

[Old_Geezer]

I guess sometimes you get 'lucky' and a defect just works, and improves the lot of the individual, and as a result, the species. Guessing again I figure the 23 to 24 match looked similar to a zip that had messed up in the middle and a tooth was stuck out unpartnered, in this case eventually to be discarded ?

[pdq1]

///I assume that it would be impossible for us to mate with great apes because the cellular mechanisms would not now be compatible because of this.///

HIV was well established in Chimps etc long before male humans contacted it. I wonder how it crossed the barrier?

[colinha]

Only exchange of bodily fluids is necessary to transfer HIV not successful reproduction.
However it looks as though meiosis is less rigid than I thought.

[wildwood]

Who is to say that pro-human animals didn't all have 23 sets and it was the now great apes that have acquired 24 sets?

Perhaps you are reading too much into the actual number of chromosomes being relative to evolution. Crayfish are quite a primitive type of animal but have 100+ sets of chromosomes.

[jake-the-peg]

pdq1

There is a considerable trade in "bush meat" in Africa

Butchering an infected ape while you have an open wound is I think a little more plausible

[pdq1]

It may be Jake but surely butchering infected apes has been going on for thousands of years. The HIV in humans was only recognised in the 1960's. It must have taken a very rare event to happen something that is out of the ordinary.

[wildwood]

pdq1, maybe many thousands of Africans died from unrecognised HIV related illnesses before 1960 but it was not felt necessary to investigate the deaths until it was transferred to Europeans.

[beso]

HIV came from the ape version which in turn came from a cat version.

Viruses frequently produce new strains some of which take off into another species.

For example bird flu H5N1 rarely infects humans because it does not effectively metabolise the sugars found in the lining of human lungs. But should it mutate and be able to feed on that sugar we are in far a very bad time.

Bingo, a new species of flu but its ancestors have been around for a long time. Similar kinds of changes happened with HIV.

[beso]

d9f1c7 // There is the XYY man for example and The XXY woman.//

This is a popular myth. A functioning Y chromosone will always result in a male because its genes produce anrogenising hormones.

The common chromosonal count mutations are extra X chromosones, sometimes even several X chromosones. One of the common most easily recognised symptoms in these men is changes in the shape of the fingers.

[beso]

The genetic evidence suggest that human line and chimp line diverged about seven million years ago. We are all descended from the products of interbreeding of the two separated lines about five million years ago.

[Jonathan-Joe]

Colin - does this help?
http://scienceblogs.c...-can-chromosome-numb/