Question on Evolution regarding Chromosomes.

[Straha]

A simple question regarding change between species:

Since different species which are connected evolutionarily have different numbers of chromosomes there must be a time when the extra chromosome develops or 'disappears' (I.E. as it has with humans compared to the great apes.) My question: Is it possible for individuals with different numbers of Chromosomes to mate successfully? And if not how do newly developing species propagate themselves if there is a chromosomal difference?

[Admiral Valdemar]

The best example of this is the donkey and horse idea, whereby you get a mule that cannot breed itself, but was formed by two species that were close enough genetically and biochemically to produce a hybrid. Other species have had this happen too.

Generally, species cannot interbreed to produce varied hybrids of your choosing. A human cannot mate with a crab, a kangaroo cannot mate with a rhino and a cockroach cannot mate with a Kodiak. There needs to be sufficient proximity at the fundamental level of the cell to allow even sterile offspring.

As to how chromosomes come about (or disappear), I believe we already have a thread on that on this very page. It can be any number of reasons.

[PainRack]

A simple question regarding change between species:

Since different species which are connected evolutionarily have different numbers of chromosomes there must be a time when the extra chromosome develops or 'disappears' (I.E. as it has with humans compared to the great apes.) My question: Is it possible for individuals with different numbers of Chromosomes to mate successfully? And if not how do newly developing species propagate themselves if there is a chromosomal difference?

Since people with Down syndrome can have healthy children.....

[Admiral Valdemar]

Down's is still within one species, though, so that's no surprise. Even with an extra or missing chromosome, the biochemistry and majority of the genome is more or less identical. For different species or sub-species, there still needs to be a fairly recent branching off, otherwise it won't work.