Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis

Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan.

The grasshopper Podisma sapporensis consists of two main chromosome races in Hokkaido. The western group of populations of P. sapporensis, belonging to the XO race, has a diploid number of chromosomes 2n = 23 in the male and 2n = 24 in the female (sex determination XO male/XX female). The eastern group of populations of this species, belonging to the XY race, differs from the western one as a result of Robertsonian translocation between the originally acrocentric X chromosome and M5 autosome in homozygous state, having resulted in the forming of chromosome sex determination neo-XY male/neo-XX female (2n = 22).
[...]
In some solitary populations (the population at the summit of Mt Yotei, populations in the vicinity of Naganuma, Oketo, and Tanno) pericentric inversions are fixed in some pairs of chromosomes, which enables marking of the discrete karyomorphes. In the Mt Daisengen population all chromosomes are two-armed as a result of fixing the pericentric inversions.

I don't know what pericentric inversions are, but I like the beat and you can dance to it.

How does it work that XX and XO come out different phenotypic sexes? Any homogametic/heterogametic system I can wrap my head around, but homogametic/haploid? What crazy quinish design do you have to do on that X chromosome so it runs that way?

I wonder how hard it is to speciate by this kind of sex-system mechanism -- one "Robertsonian translocation", it sounds like. I wonder if it could happen to people.

followup on platypus XXXXXXXXXX action

Wikipedia says (as I load it right now; I wonder if it would be feasible for them to offer timestamped links that would be resolved by groveling back through the revision-control system) that that New Scientist article didn't pick up the coolest part of the Nature article they were reporting on. The coolest part is this:

These ten chromosomes form a multivalent chain at male meiosis, adopting an alternating pattern to segregate into XXXXX-bearing and YYYYY-bearing sperm. [...] The largest X chromosome, with homology to the human X chromosome, lies at one end of the chain, and a chromosome with homology to the bird Z chromosome lies near the other end. This suggests an evolutionary link between mammal and bird sex chromosome systems, which were previously thought to have evolved independently.

Word ladder! It's a chromosomal word ladder between birds and mammals! *bounce bounce bounce*

(The Wikipedia article also says "platypi". Hmf. But I can fix that.)