🚀 go-pugleaf

In the gradual evolution of one animal species into another, how does
the chromosome count change?  For instance, if the ancestrial species
has, say, 40 chromosomes, and the emergent species has 42, does the
species go through a period in which some members have 40 and some 42?
What happens when such members mate, does the offspring have an odd
number of chromosomes?   What happens during mitosis?

What else could have happened when we see two species in the same
genera that have different chromosome counts?   Would this mean that
one of the species went through a "neck" wherein all of the from one
pair of progenators which had an aberrent chromosome count?

Are there observed species that have variable chromosome counts?  Are
there healthy, fertile humans which have nonstandard chromosome counts
because two chromosomes have aggregated or because one has split?
(Not cases where an individual got an extra copy of one chromosome.)

David Throop