Half-Male, Half-Female Fowl Explain Birds' Sex Determination

Kanan excerpts from a BBC report out of Scotland: "A study of sexually scrambled chickens suggests that sex in birds is determined in a radically different way from that in mammals. Researchers studied three chickens that appeared to be literally half-male and half-female, and found that nearly every cell in their bodies — from wattle to toe — has an inherent sex identity. This cell-by-cell sex orientation contrasts sharply with the situation in mammals, in which organism-wide sex identity is established through hormones." Kanan also supplies this link to some pictures of the mixed-cell birds.

silly

[ascari]

It's well known that birds have a completely different sex determination mechanism than mammals. For example, mammals (other than the platypus) use X/Y or X/0 chromosomes to determine sex. Birds on the other hand use Z/W chromosomes for sex determination, as do most fish, some insects and some reptiles. So the big eyed "Ooooh, who would've thunk that birds aren't handling it the way we mammals do?" attitude of the article seems kind of silly considering we've known about this striking difference for a long time. Imagine that it actually mattered... Suspect they just wanted a reason to publish those cool pictures.

Re:Changing Sex

[clone53421]

No... I’m thinking those species would have sexes which were entirely hormone-driven.

That’s basically the exact opposite of the chickens, in which sexes apparently have very little to do with hormones, and are entirely based on the genetics of the cells.

Humans would be somewhere in between. A man will grow breasts if you give him enough hormones, but you’ll have to do something surgically to change the penis...

Re:Object-sex-oriented?

[reverseengineer]

Mammals actually handle sex inheritance in an inverted arrangement from birds. Whereas mammals use the X/Y system, where males are the heterogametic type (XY) and females are the homogametic type (XX), birds (and some other animals) use a "ZW system" where males are ZZ and females are ZW. A notable feature of ZW determination is that the Z chromosome is more like a full-fledged chromosome with many genes, unlike the mammalian Y chromosome which has been paring down its genes so that it contains the sex-determining gene SRY, some genes necessary for sperm production, and little else.

This might go a long way towards explaining gynandromorphism in birds. In mammals, maleness is handled in a top-down fashion- the Y chromosome does not explicitly specify most aspects of the male phenotype, instead simply encouraging the cells that go on to make androgens, which then go on to produce a cascade of developmental effects throughout the body. In birds, the Z and W chromosomes both may have enough genes that sex determination can be handled from the bottom up, locally in each cell.

Re:What took so long?

[Chris Burke]

Seriously. What I'm inferring from the article is that you can see the difference in the cells, e.g. male vs. female....

Yeah you can see that their sex chromosomes are different.

So how the hell have they never noticed that female and male birds have these slightly different cells before, and reached the non-hormone driven conclusion before this?

Because to notice this you have to specifically study the birds who have cells that are mixed between male and female, and then notice that the sexual characteristics vary over the same organism in accordance with which cells are male and which female.

Otherwise, you're just observing that a chicken is genetically male or female, and has male or female traits. That doesn't distinguish between a per-cell sexual determination, and mammals' overall hormone-based one.

Re:Changing Sex

[Anonymous Coward]

> A man will grow breasts if you give him enough hormones, but you’ll have to do something surgically to change the penis...

The female is the base body type for humans. Everyone starts with a "female" body, but men produce chemicals called androgens that turn them into men. With things like AIS, people who are genetically male can end up with what appear to be female bodies.

So, basically, you have it backwards. The androgens make female-looking bodies into males. There's no reverse of that (e.g. you can't ungrow a penis).

Re:Interesting

[Darinbob]

What's new is that the DNA of the chicken is different on the left and right sides. It's not just developing new sexual characteristics due to hormones. If you take one of these hens that later became a rooster and checked the DNA, it would show up as female on both sides.

Re:Object-sex-oriented?

[dwye]

Your example code is cute, except that the inheritance system is more like Common LISP (inheritance from an instance) rather than C++ (inheritance from a Platonic Ideal of the class). Please rewrite appropriately.