Science Professor Fired For Teaching X And Y Chromosomes

[Ninurta]

...

In humans there are 6 common sex karyotypes: XX, XY, XXY, XXXY, & XYYY. & there are 4 rare sex karyotypes: XO, XO/XX mosaicism, XY/XXY mosacism, XXY/XXXY/XXXXY mosaicism.

In most cases, the sex of an individual is determined at birth by visual examination of the genitalia, not by karyotype testing.

Sex is also determined by the production of or the potential to produce small gametes (sperm) or large gametes (eggs).

In cases of CAIS (complete androgen insensitivity syndrome) and many with 5-alpha reductase deficiency are born with genitalia that appears female although with XY chromosomes. These (intersex) conditions are not usually discovered until puberty.

At first, I was curious as to what we were defining as "common" - 1 in 2? 1 in 5? 1 in 10? 1 in 100? One branch of my family tree had a history of intersex up to around the turn of the 19th to 20th century, when it seems to have bred itself out. Since genetics was not a thing back then, there were no records of why, and I was curious. So I looked it up, and found this:

NUMERIC ABNORMALITIES (ANEUPLOIDIES)

Aneuploidies are abnormalities affecting the number of chromosomes. The most common sex chromosome aneuploidies are 45,X (Turner syndrome); 47,XXY (Klinefelter syndrome); 47,XYY (XYY syndrome); and 47,XXX, which have birth frequencies of approximately 1 in 2500, 1 in 500 to 1 in 1000, 1 in 850 to 1 in 3000, and 1 in 1000, respectively

So in a room of 100 people, you've only got a 10% to 20% chance of finding even one of the most common of those, which is 47, XXY at 1 in 500 to 1 in 1000.

But how do those combinations affect "sex", as in the sex of an individual? Not to worry, I also found this explanation, the bottom line of which is:

In mammals, which includes humans, the Y chromosome carries a gene (SRY) that encodes a testes-determining factor. If an individual has a Y chromosome with a functional SRY gene, they will develop testes and therefore will be biologically male. Absent a Y chromosome and functional SRY gene (unless the SRY gene has been transposed to an X chromosome), an embryo will develop ovaries and will therefore be biologically female. What’s important to note is that the presence of a Y chromosome, or two, or three, etc., all result in the development of testes and therefore these individuals are biologically male. Likewise, individuals with additional or fewer X chromosomes, in the absence of a Y, all develop ovaries and are therefore biologically female.

With this in mind, the chart in the above tweet can more accurately be rewritten as:

    X – Female

    XX – Female

    XXY – Male

    XY – Male

    XYY – Male

    XXXY – Male

So no, these different chromosomal compositions are not new sexes, but rather represent natural variation within males and females. To illustrate by way of analogy, a person with Klinefelter syndrome (47, XXY) isn't a new sex in the same way that a person with Down's syndrome (who have 3 instead of 2 copies of chromosome 21) isn't a new species.

That article explains that biological "sex" is determined by the type of gametes an individual produces, or has the organs to produce, whether sperm or egg, rather than external genitalia, and that gamete production is governed by the SRY gene, usually found on the Y chromosome (but occasionally transposed to the X chromosome), rather than the chromosomes themselves.

Technically I reckon, it's really the type of sex organ - whether testes or ovaries - that an individual has, and it doesn't really matter if those testes, if present, are internal or external, or even whether or not they functionally produce gametes as far as sex determination goes.

.