Reddit reviews Animal Cytology and Evolution

Hi. I just wanted to point out that your nomenclature is incomplete. The "n" number is a genetic complexity, so no cell (other than triploids or other polyploids) are ever above 2n. You're referring to the "c" number. At the end of S prior to Meiosis-I, the cells are 2n/4c. At the end of Meiosis-I (the reductional division), they are 1n/2c. At the end of Meiosis-II (the equatorial division), they are 1n/1c truly-haploid half-genomes. Most books, and most-all online discussion, simplify the matter and just use the "n" terminology. But, particularly if you work on meiosis or chromosome dosage, this is an important distinction and experts use both "n" and "c."

( = in most organisms. There are some insects whose Meiosis-I is equatorial and Meiosis-II is reductional. But they're rare and I don't think anyone does much study on them.)

Another point, there are natural examples of diploid parthenogenesis. An organisms's (I think pill-bugs) genome can split down to 1n/1c female pronuclei in eggs, but then is laid, undergoes DNA replication, then the two haploid genome products fuse generating a diploid maternally-derived genome. White's Animal Cytology and Evolution describes all sorts of exceptions to the "normal" view of chromosome behavior.

There have been Drosophila made that have entirely-maternal genomes, although this is in an experimental context. I can't find the reference for that work now, although the guy who did it was Dan Lindsley. If you want, let me know, and I'll find it.