Chromosomal diversity is far more complex than most people tend to understand. Especially when it comes to gender and primary/secondary sex characteristics. Genetic women with Turner syndrome have only one X chromosome; they often display less-developed female sexual characteristics than other women. And people with a genetic mosaic possess XX chromosomes in some cells and XY in others. So how do we determine if they’re male or female?
Hint: Don’t say that it depends on the chromosomal makeup of the majority of their cells since women with more than 90 % XY genetic material have given birth.
Even if you get the “right” combination of sex chromosomes, it’s no guarantee that you’ll fit into the carefully circumscribed human definitions of male and female. For example, genetic women (XX) with congenital adrenal hyperplasia produced unusually high levels of virilizing hormones in utero and develop stereotypically masculine sexual characteristics, including masculinized genitals. SRY, discovered in 1989, is a small gene located at the tip of the short arm of the Y chromosome.
So what does it do?
Actually, like all genes, it does nothing except to act as a blueprint for a protein.
In this case, the protein of the same name does funky things to DNA, like bending it and unwinding the 2 strands, so that other proteins can get in and attach themselves to other genes that are then turned on. So how did this gene get its reputation (and its name) as the “sex-determining” gene? Similarly, genetic men (XY) with complete androgen insensitivity syndrome don’t respond to male hormones and fail to develop masculine sexual characteristics. Most live their lives as women. Some historians suggest that Joan of Arc, Elizabeth I and Wallis Simpson all suffered from this syndrome.
So what’s the answer?
There isn’t one, at least if we’re looking for the answer in biology.
We must not fall back on biology.
Rather, we must always remember that it is we, not biology, who decide who counts as male or female.
And it is we who must take responsibility for our decisions.
SRY, discovered in 1989, is a small gene located at the tip of the short arm of the Y chromosome. So what does it do? Actually, like all genes, it does nothing except to act as a blueprint for a protein. In this case, the protein of the same name does funky things to DNA, like bending it and unwinding the 2 strands, so that other proteins can get in and attach themselves to other genes that are then turned on. So how did this gene get its reputation (and its name) as the “sex-determining” gene? As is pretty common in the world of genetics, this was because of some errant mice. Researchers in England took a laboratory-made copy of this gene and inserted it artificially into a female (XX) mouse embryo at a very early stage of development. The mouse was “converted” from female to male, so the gene must have been responsible – right? Well, maybe not. A few years later, a similar gene was found on human chromosome 17. When the important part of this gene was inserted into a female mouse embryo, the same thing happened. Voila! A male.
So now we have 2 genes that can turn a female into a male, and one of them is not located on the Y chromosome! How can that be? It turns out that SRY is probably just a facilitator that allows a more critical gene (or genes) to function, by blocking the action of another opposing factor. Can the magic of genetics do the opposite – turn a male into a female? Indeed it can. A gene on the X chromosome (the chromosome one typically associates with “femaleness”) called DAX1 when present in a double copy in a male (XY) mouse, turns it into a female.
So now we have genes on the Y that can turn females with XX chromosomes into males and genes on the X that can turn males with XY chromosomes into females…
Maleness and femaleness are NOT determined by having an X or a Y, since switching a couple of genes around can turn things upside down!
In fact, there’s a whole lot more to maleness and femaleness than X or Y chromosomes. About 1 in 20,000 men have no Y chromosome, instead, they have 2 Xs. This means that in the United States there are about 7,500 men without Y chromosome.
The equivalent situation – females who have XY instead of XX chromosomes – can occur for a variety of reasons and overall is similar in frequency.
For these 15,000 or more individuals in the US (and who knows how many worldwide), their chromosomes are irrelevant.
It is the total complement of their genes along with their life experiences (physical, mental, social) that makes them who they are (or any of us, for that matter).
The last time I counted, there were at least 30 genes that have been found to have important roles in the development of sex in either humans or mice. Of these 30 or so genes 3 are located on the X chromosome, 1 on the Y chromosome and the rest are on other chromosomes, called autosomes (on chromosomes 1, 2, 3, 4, 7, 8, 9, 10, 11, 12, 17, 19).
In light of this, sex should be considered not a product of our chromosomes, but rather, a product of our total genetic makeup, and of the functions of these genes during development.
Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex; for example, XX males or XY females (see androgen insensitivity syndrome). Additionally, an abnormal number of sex chromosomes (aneuploidy) may be present, such as Turner’s syndrome, in which a single X chromosome is present, and Klinefelter’s syndrome, in which two X chromosomes and a Y chromosome are present, XYY syndrome and XXYY syndrome. Other less common chromosomal arrangements include: triple X syndrome, 48, XXXX, and 49, XXXXX.
Gender identity is one’s personal experience of one’s own gender.
Gender identity can correlate with assigned sex at birth, or can differ from it.
All societies have a set of gender categories that can serve as the basis for the formation of a person’s social identity in relation to other members of society. In most societies, there is a basic division between gender attributes assigned to males and females, a gender binary to which most people adhere and which includes expectations of masculinity and femininity in all aspects of sex and gender: biological sex, gender identity, and gender expression. In all societies, some individuals do not identify with some (or all) of the aspects of gender that are assigned to their biological sex; some of those individuals are transgender, genderqueer or non-binary. There are some societies that have third gender categories. Some studies have investigated whether or not there is a link between biological variables and transgender or transsexual identity.
Several studies have shown that sexually dimorphic brain structures in transsexuals are shifted away from what is associated with their birth sex and towards what is associated with their preferred sex.
In particular, the bed nucleus of a stria terminalis or BSTc (a constituent of the basal ganglia of the brain which is affected by prenatal androgens) of transwomen is similar to cisgender womens and unlike mens.
Similar brain structure differences have been noted between gay and heterosexual men, and between lesbian and heterosexual women. Another study suggests that transsexuality may have a genetic component. Research suggests that the same hormones that promote differentiation of sex organs in utero also elicit puberty and influence the development of gender identity. Different amounts of these male or female sex hormones within a person can result in behavior and external genitalia that do not match up with the norm of their sex assigned at birth, and in a person acting and looking like their identified gender. For many people, biology defines sex, and sex is always a binary affair. Sure, postmodernists have been playing with the concept of gender for decades, but sex, well, sex is sacred, which means you’re either biologically male or female. But never both. Or neither.
Biology doesn’t work that way.
Biological phenomena don’t necessarily fit into human-ordained binary categories.
So while humans insist that you’re either male or female – that you have either XY or XX sex chromosomes – Biology begs to differ.
For example, genetic men with Klinefelter syndrome possess an extra X chromosome (XXY) or more rarely, two or three extra Xs (XXXY, XXXXY); they typically produce low levels of testosterone, leading to less-developed masculine sexual characteristics and more-developed feminine characteristics than other men. In contrast, some men receive an extra Y chromosome (XYY) in the genetic lottery, and while they have been referred to as “supermales” that is more sensationalism than science. The idea remains the same though, we are more than just our chromosomes, and that in both beauty and complexity, is something worth believing in.