Understanding the Genetics of Speciation

Are there any examples of species with differing numberer of chromosomes that continue to successfully interbreed?Using man as an example, at some point several million years ago, we lost a chromosome from our contemporaries (chromosome 2 fusion I believe). There must have been a 'first specimen' that had this mutation, and this single ancestor must still have been able to reproduce in order to spread this mutation.Are there any modern examples of this process occuring, where we can see a chromosomal change mutation spreading throughout a species?