Human & ape chromosome count

[technetium]

Hi biology types,

Humans have 23 pairs of chromosomes while orangutans, gorillas and chimpanzees have 24. Presumably our common ancestor had either 23 or 24 pairs.

My question is how could the very first individual with a different chromosome count have arisen and then go on to found a new line, given that the probability of two such individuals meeting at the same time would be virtually zero?

Also as there is no doubt amongst the thinking public that humans & apes do share a common ancestor I have to assume that chromosome count is not particularly relevant because given the number of species in the animal kingdom there must be many examples of completely different species having the same number of chromosomes?

 

[dbnp48]

Hi biology types,

Humans have 23 pairs of chromosomes while orangutans, gorillas and chimpanzees have 24. Presumably our common ancestor had either 23 or 24 pairs.

Here's a link with more info:
http://en.wikipedia.org/wiki/Chimpanzee_genome_project

My question is how could the very first individual with a different chromosome count have arisen and then go on to found a new line, given that the probability of two such individuals meeting at the same time would be virtually zero?

Hundreds of millions of years.

Also as there is no doubt amongst the thinking public that humans & apes do share a common ancestor I have to assume that chromosome count is not particularly relevant because given the number of species in the animal kingdom there must be many examples of completely different species having the same number of chromosomes?

Horse and donkeys have different numbers of chromosomes and can be bred to produce either a mule (horse is mother) or a hinny (donkey is mother). Here's a link:
http://en.wikipedia.org/wiki/Mule
There are several other examples of hybids.

 

[Cifo]

how could the very first individual with a different chromosome count have arisen and then go on to found a new line

This also puzzles me. How can one individual (or even a pair) generate enough genetic diversity (that is, "minimum viable population size") for, not only a new species to survive, but also prosper? I can see a genetically different rabbit, fish or ant producing dozens or thousands or millions of offspring, but what about humans or elephants that typically produce only a few offspring in their lifetime?

This seems to pit genetic diversity against evolution.

 

[river-wind]

Bottlenecks in viable reproductive population are dangerous for the survival of a line, but not a complete roadblock. Internal lack of diversity can risk the population, but look at the cheetah - so long as the current genetic form is functional, continuing addition of random mutation to each subsequent generation can will in diversity over time.

As for the OP; hybrids have been addressed, but also keep in mind that such a duplication error, if not detrimental to the individual, may happen multiple times from the same parent. Given that inbreeding/incest is not an issue with apes, if a male and female from the same parent held the same mutation, then no hybridization would be needed, and a split could be possible in a single generation. Such duplication is most often neutral or negative to the individual's health, but not always.

 

[billvon]

My question is how could the very first individual with a different chromosome count have arisen and then go on to found a new line, given that the probability of two such individuals meeting at the same time would be virtually zero?

Because the first heterogeneous organism was probably still fertile, and could still interbreed with the prototype. That would start propagating the new chromosome count.

Note that even with zebra/donkey hybrids, some female offspring are fertile.

 

[Fraggle Rocker]

Note that even with zebra/donkey hybrids, some female offspring are fertile.

They used to be called "zebrasses" but now people prefer the name "zonkey."

 

[river-wind]

I still prefer zebrass.