Human / Primate Chromosones

[Claude_Remains]

We have 23 pairs. They have 24 pairs. We have a pair that mutated and formed one?

[Claude_Remains]

And so much for " if 23 is good - 24 is better"

[Claude_Remains]

Chromosomes- I know, sorry bout the typo.

[Saint_Cad]

IANAB but one will probably be along shortly
IIRC two of the primate chromosomes joined to make one in us. I believe it is chromosome. An interesting question is what if we resplit it? Paging Dr. Mureau!

[Uncertain]

The organization of the genome into chromosomes changes all the time (on an evolutionary time scale). Pieces move from one chromosome to another (tranlocations), pieces invert, chromosomes split and fuse. In this case, since gorillas and chimps have the 48 arrangement, it seems fairly clear that there was a fusion event in the line leading to humans. And we know which chromosomes were involved (chromosomes A and B in other apes correspond to chromosome C in humans, but I don’t know off-hand what A, B, and C are).

[Smeghead]

It’s the human chromosome 2 that’s the fusion product. IIRC, the corresponding chromosomes in nonhuman primates are called 2a and 2b, but that’s a fuzzy memory.

[Superfluous_Parentheses]

Kenneth Miller on Common Ancestry with Apes

[qazwart]

@Claude_Remains

We have 23 pairs. They have 24 pairs. We have a pair that mutated and formed one?

That’s actually the truth. Two chromosomes merged into one in homo sapiens. I can’t remember which one, but the end of a chromosome has a special end marking, and one of our chromosomes has this marking in the middle.

I found this out by reading the transcripts of the Dover case. They should publish those transcripts in a book with commentary. They’re fascinating reading, and very educational.

[Darwin_s_Finch]

From the Wikipedia article on chromosome 2:

All members of Hominidae except humans have 24 chromosomes. Humans have only 23 chromosomes. Human chromosome 2 is widely accepted to be a result of an end-to-end fusion of two ancestral chromosomes. [3][4]

The evidence for this includes:
[ul]
[li] The correspondence of chromosome 2 to two ape chromosomes. The closest human relative, the bonobo, has near-identical DNA sequences to human chromosome 2, but they are found in two separate chromosomes. The same is true of the more distant gorilla and orangutan. [5][6][/li] [li] The presence of a vestigial centromere. Normally a chromosome has just one centromere, but in chromosome 2 we see remnants of a second. [7][/li] [li] The presence of vestigial telomeres. These are normally found only at the ends of a chromosome, but in chromosome 2 we see additional telomere sequences in the middle. [8][/li][/ul]

Chromosome 2 is thus strong evidence in favour of the common descent of humans and other apes. According to researcher J. W. IJdo, “We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2.”[8]

[ShibbOleth]

I’m not wearing my glasses and I read the thread title as “Human / Pirate Chromosomes”.

That is all.

[Alex_Dubinsky]

@Uncertain

The organization of the genome into chromosomes changes all the time (on an evolutionary time scale). Pieces move from one chromosome to another (tranlocations), pieces invert, chromosomes split and fuse. In this case, since gorillas and chimps have the 48 arrangement, it seems fairly clear that there was a fusion event in the line leading to humans. And we know which chromosomes were involved (chromosomes A and B in other apes correspond to chromosome C in humans, but I don’t know off-hand what A, B, and C are).

How the hell does that work, exactly? If you’re the first animal with the fused chromosomes, how is that trait distributed to the rest of the population? Can you breed with normal-choromosomed individuals just fine? Is there a way for the fused-chromosome trait to be selected for? (What’s the probability of it being passed on, anyway?)

[Colibri]

@Alex_Dubinsky

How the hell does that work, exactly? If you’re the first animal with the fused chromosomes, how is that trait distributed to the rest of the population? Can you breed with normal-choromosomed individuals just fine? Is there a way for the fused-chromosome trait to be selected for? (What’s the probability of it being passed on, anyway?)

In intial stages, if you have a cross between an individual with a fused chromosome pair and another with separate chromosomes, the fused chromosome will still generally pair up OK with its matched chromosomes during meiosis, because most stretches of DNA will still be the same. The trait of fused chromosomes could be selected for in a small population, due to the fact that the position on a chromosome can have effects on gene activity on that chromosome. If these changes in activity are beneficial, the trait will spread.

Once the trait has been established in an isolated population, differences in other genes may accumulate. If the population comes back into contact with another population with unfused chromosomes, these gene differences could prevent the fused and unfused versions from pairing up properly during meiosis. This can result in hybrid sterility, as in the case mules, where the parent species, horses and donkeys, have different chromosome numbers. Once this happens speciation has occurred.