PZ Myers: Basics: How can chromosome numbers change?

On Pharyngula, PZ Myers treats us with an incredibly accessible explanation why chromosome number can change.

The posting was in response to an email PZ received about the evolution of chromosome numbers.

How did life evolve from one (I suspect) chromosome to… 64 in horses, or whatever organism you want to pick. How is it possible for a sexually reproducing population of organisms to change chromosome numbers over time?

Firstly: there would have to be some benefit to the replication probability of the organisms which carry the chromosomes

…

Secondly, the extra chromosomes need to come from somewhere. I’m not sure about this, but I believe chromosome number are not determined by genes, are they? …

PZ presents us with an outstanding overview of the science involved and shows us how good science can help address the questions raised by those interested in biological science as well as address the misrepresentations of science by creationism.