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.

Comments

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: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.