Lizzie: breeding mutant flies says:
ok ... we didn't look at hermaphrodites per se
Lizzie: breeding mutant flies says:
but we did look at XY females, and XX males
»｡::Kunama::｡« - research >_< says:
*blink*
»｡::Kunama::｡« - research >_< says:
... ?!
Lizzie: breeding mutant flies says:
what's the question?
Lizzie: breeding mutant flies says:
we were studying the human sex determining system, and the easiest way to find out about it is to look at instances in which it has gone wrong
Lizzie: breeding mutant flies says:
since we can't ethically experiment on human sex determination
»｡::Kunama::｡« - research >_< says:
yes, an XY female would be where it's gone wrong... do they end up dead, or ..?
Lizzie: breeding mutant flies says:
no, they end up female :P
»｡::Kunama::｡« - research >_< says:
wtf? :S
Lizzie: breeding mutant flies says:
sex is not exactly vital to life
Lizzie: breeding mutant flies says:
you can have one, the other, both, or neither, and still live
Lizzie: breeding mutant flies says:
okay, it will help if you understand about X-chromosome inactivation
Lizzie: breeding mutant flies says:
you see, for most chromosomes, if you have too many, you die
Lizzie: breeding mutant flies says:
because you get too high a dose of all the gene products from that chromosome
Lizzie: breeding mutant flies says:
chromosome 21 is an exception - it is very small, and has very few genes
Lizzie: breeding mutant flies says:
so if you have an extra copy of that, you don't die - you just end up with Down's Syndrome
»｡::Kunama::｡« - research >_< says:
eww.
Lizzie: breeding mutant flies says:
that should give you an idea of how severe a chromosomal mutation is
Lizzie: breeding mutant flies says:
right?
Lizzie: breeding mutant flies says:
now, human males can get by with only one X chromosome, but human females have 2
»｡::Kunama::｡« - research >_< says:
mmm.
Lizzie: breeding mutant flies says:
so how do females deal with the extra X? It gets inactivated
Lizzie: breeding mutant flies says:
mostly
Lizzie: breeding mutant flies says:
small parts of it remain active - just enough to balance about the same level of gene expression as you get from the tiny Y chromosome
Lizzie: breeding mutant flies says:
this system is so good that it can even deal with more X chromosomes
Lizzie: breeding mutant flies says:
someone with genotype XXXXY will develop into a pretty healthy male
Lizzie: breeding mutant flies says:
although that's uncommon
»｡::Kunama::｡« - research >_< says:
o.o
Lizzie: breeding mutant flies says:
XXY is fairly ommon, though
Lizzie: breeding mutant flies says:
*common
Lizzie: breeding mutant flies says:
with no ill effects
»｡::Kunama::｡« - research >_< says:
here, we have the specimen, 'bishounen', of genotype XXY.
Lizzie: breeding mutant flies says:
ha
»｡::Kunama::｡« - research >_< says:
teehee.
Lizzie: breeding mutant flies says:
the double X doesn't make them more girly at all
Lizzie: breeding mutant flies says:
(alas)
Lizzie: breeding mutant flies says:
in fact, it's the Y chromosome which is the genetic 'switch'
Lizzie: breeding mutant flies says:
so in XY females, the switch doesn't get flicked properly ... and in XX males it gets flicked when it shouldn't have been
Lizzie: breeding mutant flies says:
one cause of XY fmales is a disorder known as androgen insensitivity syndrome (AIS). Basically, there is a receptor in our bodies that testosterone binds to in order to exert its effect. People with AIS don't have that receptor
Lizzie: breeding mutant flies says:
so they don't get the effects of testosterone
»｡::Kunama::｡« - research >_< says:
oh, ok.
Lizzie: breeding mutant flies says:
even if they have a Y chromosome, they develop as females
Lizzie: breeding mutant flies says:
(but not quite right - they're infertile, and their vagina doesn't develop properly. Also, they don't get pubic or underarm hair.)
»｡::Kunama::｡« - research >_< says:
that makes sense then.
Lizzie: breeding mutant flies says:
usual cause of XX males is that a piece of the Y chromosome has become attached to one of the autosomes (non-sex chromosomes). So they're secretly XXY.
»｡::Kunama::｡« - research >_< says:
that's weird.
»｡::Kunama::｡« - research >_< says:
but that does explain why they turn out male.
Lizzie: breeding mutant flies says:
translocations from one chromosome to the other are actually quite common
Lizzie: breeding mutant flies says:
they often happen, with no ill effects
Lizzie: breeding mutant flies says:
or effects that are hard to oobserve - like lowering fertility
»｡::Kunama::｡« - research >_< says:
bwahaha
although that is fairly logical too.
»｡::Kunama::｡« - research >_< says:
if you're faulty, it makes sense that there's less chance of passing it on
Lizzie: breeding mutant flies says:
that's a bit of a simplistic way of thinking about it ... the point is that you have to pass on a balanced set of chromosomes
Lizzie: breeding mutant flies says:
You have two copies of each chromosome. If, say, a bit of one of your chromosome 4s attached to one of your chromosome 8s, then you either have to pass on your normal pair, or your translocated pair. If you pass on the foreshortened ch.4 without the extra-long ch.8, the kid will be missing some genes
»｡::Kunama::｡« - research >_< says:
o.o
»｡::Kunama::｡« - research >_< says:
those ones have faults.
Lizzie: breeding mutant flies says:
and if you pass on the extra-long 8 with the normal ch.4, the kid will get an overdose of some genes
»｡::Kunama::｡« - research >_< says:
death~!
»｡::Kunama::｡« - research >_< says:
... possibly.
Lizzie: breeding mutant flies says:
possibly!
Lizzie: breeding mutant flies says:
the point is, half the sperm/eggs will be viable (they'll either have a normal set of chromosomes, or the balanced translocation) and half will be unviable (they have an unbalanced set).
Lizzie: breeding mutant flies says:
so that cuts fertility in half, but doesn't make you completely infertile
Lizzie: breeding mutant flies says:
these things are common precisely because you CAN pass them on pretty easily
»｡::Kunama::｡« - research >_< says:
... which explains in part the number of stupid people in society.
Lizzie: breeding mutant flies says:
...
»｡::Kunama::｡« - research >_< says:
teehee.
Lizzie: breeding mutant flies says:
these people are perfectly healthy! And probably smart!
Lizzie: breeding mutant flies says:
I'm sure there's a better thing we can blame for stupidity
Lizzie: breeding mutant flies says:
like TV, or schools
»｡::Kunama::｡« - research >_< says:
yeah. Numerous things.
Lizzie: breeding mutant flies says:
so, have I satisfied your curiosity about sex determination?
»｡::Kunama::｡« - research >_< says:
no... but I lost interest at some point...
Lizzie: breeding mutant flies says:
heh
Lizzie: breeding mutant flies says:
fair enough
Lizzie: breeding mutant flies says:
if you have a more specific question than "how are hermaphrodites made", I might be able to help