pz

About 1 in 20000 males born are XX. The most common cause is a heteromorphic X carrying a translocation of SRY.

Since the development of both male and female sexual characteristics in mammals are dependent on global hormonal signals, you can trans-sex the developing embryo either way by suppressing or adding hormones.No, this is a gross oversimplification. There is an early morphologically undifferentiated state which resembles the female state only in the sense that it lacks an obvious couple of bumps. It requires just as much elaboration during development to turn that into a female as it does to turn it into a male.Err, what?

tronvillain

You know, the saddest thing is that I used to know that? It all came rushing back to me. *chuckle* Of course, the occurence of an XX male usually requires a crossover between the X and Y chromosomes during meiosis (putting part of the Y chromosome on the X chromosome - the SRY as you pointed out), while the occurence XY females usually simply requires inactivation of regions of the Y chromosome (which is what I meant by "female is default). Oh, and you have to look at what I was responding to to make sense of the last thing.

Oh, and can you actually make totally functional XX males simply by appropriately varying hormones during fetal development?

RufusAtticus

Yes because IIRC SRY is responsible for producing testostrone in large quanties to produce external male sexual characteristics. However, not all male sexual characteristics come from SRY. Some of them result from chromosome counting, i.e. comparing the number of X-chromosomes to autosomal chromosomes.

tronvillain

Wouldn't that be a no then? I asked if you could make a totally functional male, not only one possessing external male sexual characterstics.

Happy Wonderer

Actually it is sort of interesting, XX males are usually infertile but I found one study here that if I understand correctly shows a series of mutations in mice that can transform XX males into fertile.

I can't tell from the abstract if these fertile XX males would ever produce male offspring. My assumption in my previous post was that they wouldn't, however with this mutation I suppose it is possible that XX' offpspring could be fertile -- so what do we have, a new sex? And if their female grandchildren mate with a normal male... Oh my goodness that could get interesting if all the combinations are viable.


hw

tronvillain

Well, that is interesting, but it is not due to external hormonal manipulation.

Pantera

Someone has to post a link to this

Penis and vagina as proof of God?

Happy Wonderer

You are thinking too much like an engineer. This is a thought experiment, not a feasibility study. I'm certainly not advocating that parents who want to ensure that they have male children take hormones to affect the sex of the zygote, and I'm not even sure what the viability of the 'species from a single female human' has to do with the origin of sexual reproduction. I should probably have phrased my answer to the "which came first" question differently (open to suggestions.)

However it is a lazy, hot day and it is kind of fun to mull over, especially if I can snag some more real science from the gurus here.

XX males are fully functional with the exception of fertility - many of them do not know that they are genetically female until they go to a fertility clinic. The interesting question is if there is something that would be contributed by the father's Y chromosome that would be missing in XX. If that were the case, then my hypothetical female would have no way to create a male child other than by somehow creating a Y chromosome. From the thought-experiment point of view, that would be cheating...

This study seems to me to imply that at least some XX males in some species are fertile. These XX males would not be passing along any Y chromosome (by any mechanism understood at least) to their offspring, so assuming that their offspring are fertile then at least some mutant forms of my hypothetical female have everything they need to produce male children by hormonal manipulation. Thus, the vagina could be said to 'come first.' (Don't even touch that pun. Er. *blush*.)

Of course this is all pretty roundabout, clownfish are a much better non-imaginary example that shows that you can have sexual reproduction without genetic differences between the 'sexes.'

(Layman's language breaks down trying to describe this stuff, I mean 'male' clownfish are not really male are they? Of course they are. No they aren't! Arrgh...)

hw