Do phylogenetically close species have cells with similar chromosome counts?

Answer 1

That depends on the species! For example, humans and some of their closest relatives - excluding chimps and bonobos - actually do not have the same number of chromosomes! We do have the same number of chromosomes as chimps and bonobos, but not the other great apes.

The reason for this is fascinating - somewhere along our divergence from these apes, two of the chromosomes merged together to create one, larger, chromosome. So, we (and chimps and bonobos) actually have 23 pairs of chromosomes, or 46 total chromosomes. Other great apes have 24 pairs, or 48 total chromosomes.