okay - basic biology question...

[loveyouradvice]

Am I right in thinking that from the very first second ie a one cell embryo they are either XX or XY?

Interesting discussion at lunch with well=informed woman who was quite convinced by the hormone washes determining sex later on in pregnancy.

Sorry this is biology 101 but I just needed to check...

An egg has an X, and a sperm has an X or a Y... So sex is determined at the point of conception.

You are correct.

The sperm arrives with either an X or a Y chromosome and whichever it is determines the sex of the embryo.

Yup!

All depends on whether the sperm which fertilizes the egg carries an X or Y chromosome.

Well-informed my arse.

There is some (unverified) suggestion that hormones during pregnancy might affect masculinity or femininity. So if you believe in gendered souls, then you might believe gender can be affected by hormone washes.

The answer to the question s phrased it is 'maybe' - as not everyone is either XX or XY.

But it's also 'yes'to your subsequent question that the individual's chromosomes are fixed at the moment of conception.

However the epigenetics may be influenced by environment, including uterine environment, so it is possible (and still a fairly new field of study) that expression of X or Y linked characteristics could be influenced.

Sex determined at conception as stated above. Genitals visibly differentiated by 11 weeks gestation.
Makes a mockery of all that “assigned at birth” crap, doesn’t it!

I think I read that the Y chromosome doesn't start to express itself (and differentiate the fetus) until later on, about 6 weeks I think.

But the "path" that the fetus is put on is determined at conception by the X or Y sperm. The Y just doesn't cause a diversion (I am using traffic terminology for some reason! I'm not a biologist...) until 5-6 weeks when development goes down a different route than an XX one would.

Hopefully one of our resident scientists can explain if I've understood properly

Technically - if I'm being a pedantic arse - whether the individual sperm will be carrying an X or a Y is determined at spermatogenesis - each individual sperm is already a boy sperm or a girl sperm before conception.

Its basically because there aren't any sex differences in a cluster of cells in the early stages of development. The fetus is growing a brain and the start of the central nervous system, arms and legs.

The answer to the question s phrased it is 'maybe' - as not everyone is either XX or XY.
Everyone has at least one X chromosome.
People with anything other than XX or XY suffer a genetic condition. They will have various physical symptoms. It's similar to people with Downs syndrome.

There are various disorders of sexual development but they don't have anything to tell us about trans - because trans people have standard XX or XY chromosomes

That’s right Sonic. Although the chromosomes are defined at conception, sex included, male and female foetuses develop in exactly the same way initially. That’s why males have nipples.

Well at about 3 days post conception (ivf) it is possible to tell the sex, because you can select for sex-linked diseases this way.

Iirc (it's not an experiment I have actually tried ), if you stick a load of sperm in a centrifuge, the x's will sink and the y's float, as the x's are marginally heavier than the y's. Apparently this is how they select for sex in some animal breeding, or at least how they used to.

I'm not sure how you gender-select for lady brains, breeding-wise...

Embryo development of other animals in comparison with humans is fascinating - they look very similar. Don't think anyone is using this as proof of trans-speciesism though.

Each egg has an X chromosome. Each sperm has either an X or a Y chromosome. So sex (XX or XY) is determined when the egg is fertilised. Male and female embryos develop in the same way for the first 7 weeks, after which male and female sex organs start to differentiate. So, for instance, a 6 week old XY embryo and a 6 week old XX embryo will appear identical, but they are internally programmed to adopt different fates.

Intersex conditions are very rare and should not be used by trans activists of proof of anything. I think trans activists have sometimes used the language of treatment for intersex people. For example in the past before genetic testing (which these days can distinguish and clarify an intersex person’s genetic identity from a very young age) there might have been some confusion as to a baby’s sex and in those cases they would be “assigned” a sex which might have included surgery as a baby or child. My understanding is that is no longer considered appropriate or ethical and instead decisions on that individual’s bodily integrity should be made by them.

So the irony is that as we have grown to respect intersex people’s own autonomy and bodily integrity to make these choices for themselves, usually as adults, we are removing the same from children identified as “trans”.

Please correct me if my understanding of these issues is wrong. DH is a doctor and that is my understanding after discussions with him.

You are correct that sex is determined at conception. However the differentiation of sex organs takes place some weeks into the pregnancy. If the SRY gene is present (on the Y chromosome), you'll get male anatonomy and the precursors for male gamete in the embryo, if there is no SRY gene, you get female anatomy and the precursors for female gamete (eggs) in the embryo. This differentiation involves 'hormone washes'. This is when everything goes right. Intersex conditions happen, when something goes wrong.

In case of intersex conditions, you might for example have the rare case that the organism is XY but is insensitive to the male hormones that play a role in differentiation. That may in the extremest case mean the body's cells are XY, but the organism develops a vagina and the baby looks like a girl (Swyer Syndrome). This condition leads to infertility. There are no functioning ovaries. The condition demonstrates well the difference between sex determination (XY) at conception, versis sex differentiation (in this case gone wrong because of a genetic insensitivity).

make that 'because of a genetically caused hormone insensitivity' (this genetic problem was also programmed into the cells since conception).

Phew... started to doubt myself...

SRY stands for sex-determining region Y protein, so that’s a pretty good indication of what it does. It’s usually found on the Y chromosome but it can cross over to the Y and that’s what causes Swyer syndrome, where someone is ‘karyotypically’ male but ‘phenotypically’ female.

XX (female) and XY (male) are the usual karyotype. Karyotype just means your arrangement of X and Y chromosomes. Phenotype refers to how your genes are expressed, eg male or female, blonde, ginger, brunette, blue eyed, brown eyed, whatever.

TRAs will try to baffle you with XXX, or XYY, XO, and a bunch of other karyotypes, but they have nothing to do with transgenderism; they generally effect things like fertility, if anything at all.

Most XYY men will never even know because there are so few genes on the Y chromosomes that having multiple copies doesn’t matter. Years ago it was proposed that it lead to increased criminality but that’s horseshit.

She probably saw Kellie Maloney on Loose Women explaining the "hormone wash" theory - that's where I saw it, anyway

This is a really interesting thread.

It says a lot about the TRA organisations that they keep mentioning intersex, when repeatedly asked not to by people with intersex conditions. Tells you which group of people is the only group to be able to order others to pander to their identity.

That theory should be renamed the 'hormone hogwash theory'.

Hormone washes are, as far as this academic developmental biologist is concerned, nonsense.

There are conditions caused by inappropriate levels of maternal hormones - usually high T affecting baby girls.

The growing fetus will produce its own hormonal environment.

But ‘washes’ produced by Mum that exist to direct sex differentiation in baby? Nope.

Of course if we want to talk about hormone exposure in pregnancy leading to intersex conditions, I don’t think the research re effects of synthetic oestrogen in effluent water (off the top of my head...) will be very beneficial to the pro-transing side.

The effects of hormone containing waste on the environment are an argument against medical transition!