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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.
That's somewhat close to the rate of intersex conditions in mammals, including humans.
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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.
Okay, but knowing that the nature of the sex chromosomes is different isn't the same as knowing that the overall mechanism by which the sex of the organisms is determined is different. The assumption was that it was still essentially the same -- sex chromosome in the egg cell ends up controlling the formation of male or female gonads, which then release male or female hormones, which then control the sexual characteristics of the organism as a whole. And this is pretty reasonable on its face, since chickens do develop male/female gonads which do release sex hormones. It's largely the same, right up to the point where those hormones are what determine sex for every cell or not.
In mammals that's the case. Every cell in your body could be carrying X/Y chromosomes, but if due to some disorder you aren't producing male hormones but instead female ones, you will acquire female secondary sexual characteristics.
Now we know this isn't the case for birds, that every cell has its own sexual identity independent of hormones, and no we have not known about this striking difference until now.
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Also, when a flock of chickens suddenly loses it's rooster, the dominant female will sometimes act as a rooster. That isn't hormonal?
This does happen.
Apparently this is not all that common, that is, not every hen can become a henry, and perhaps TFA suggests the means by which this does happen when it does.
Apparently One in 10,000 hens can change sex, usually in response to a gonad ceasing to function. One professor explained it this way:
"Yes a type of sex reversal does occur in poultry. Both a right and left ovary start to develop in the embryo but between day 7 and 9 of incubation the right gonad ceases to continue development. If in the adult, the left ovary is removed or fails to function the right gonad hypertrophies to become a testis-organ and thus "a male' instead of what was a hen."
The implication of this is with regard to TFA is that failure of one gonad cease development leads to the double expression of traits documented in the story.
So there is nothing new here that hasn't been known for some time with regard to chicken sex other than that the normal failure to enter stasis can lead to odd birds.
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that was meant to be a wikipedia link, something weird happened when I did a preview, edited again, and submitted (I had missed a closing quote before the first preview, but I think that caused slashdot to munge the URL, but I was going quickly). In any case you can search on that in wikipedia.
My point is there are lots of ways to do sex determination. Echidnas and Platypuses are particular weird in this way (and in every other way), even though they are mammal they don't use XY.
And of course, in the most literal real world sense, it is all inherited from instances.