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

[eub]

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.

Comments

[jinian.livejournal.com]

The story goes that it already is happening to people, in that y'all's Y chromosome is getting smaller and smaller over time. When it gets small enough, I imagine the guy who comes out functional as X0 is going to have the reproductive advantage.

As it stands, there's a heck of a lot of masculinizing activity coming out of the SRY gene on the Y chromosome. It's possible that no human genome can make a successful male without that, but things happen. Suppose a very small Y chromosome, being somewhat at loose ends in meiosis, attached itself to chromosome 21, and male became the default expression for that organism? Then it's an easier step to find feminizers for that line, which should still be interfertile with the rest of the human race. For all we know, it's happened already. :)

Feminization could occur the same way incomplete dominance does; one allele doesn't produce enough hormones to make you female, but two do. Probably they'd both stay active then instead of a random (if it really is) choice becoming a Barr body, which would be another interesting mutation. Or the Barr body would affect which genes were expressed on the other X, which is entirely likely and why did I think of the rest of this anyway when that's so sensible?

[jinian.livejournal.com]

Incidentally, bee males are actually, all-the-way haploid, not just X0. They have no fathers. Neat stuff.

[eub.livejournal.com]

*aerial sparkles*

Blushingly, what's a Barr body? Ah, the web says what it is, the inactivated X chromosome, but not all about how they work. How do they do the affecting which genes are expressed on the other?

[eub.livejournal.com]

Oh, I forgot about bees. Now I wonder how they work too.

Blushingly, what's the difference between haploid and XO?

[jinian.livejournal.com]

In my head, which is the only place they're known to do it, a Barr body would not be completely methylated/histone-deacetylated (dormant), because really it doesn't have to be that way; some of its genes would handwavily make promoters go on the other X. It's all handwaving at that level really, even for the textbooks' new editions, though we're really going places quickly.

[jinian.livejournal.com]

As you know, Bob, haploid organisms have n chromosomes, while diploid have 2n. Diploid but using XX/X0 sex differentiation organisms will have 2n and 2n-1 repectively. (That is a zero, by the way, not an O.)

Bees are weird, man. I hope to take entomology soonest. The 1942 Essig College Entomology text has, not surprisingly, little on genes.

[eub.livejournal.com]

I think I understand. That sounds promising.

[eub.livejournal.com]

Oh! I was zoomed in too far. Thanks.

O/0. Thanks also. Newfangled non-slashy zeros these days.

1942: heh.

[hattifattener]

bees = moss !

[eub.livejournal.com]

drone moss?

[jinian.livejournal.com]

More on the loss of the Y chromosome and possible function after that. He doesn't seem to have heard about Kayuga mouse, though.

[eub.livejournal.com]

I hadn't heard either. Cool.

Reading along wondering what had happened with older mammal species, and then he mentioned the mole vole. Nifty. Want data on other species, too.