Biology / gender / gene / Genetics

Breaking Down a Binary: New Research Suggests a Spectrum of Biological Sexes

By: Tiago Palmisano

Edited by: Josephine McGowan 

The discussion of gender identity has seen a sharp increase in recent years. As social stigma fades and scientific understanding increases, those who do not identify with the traditional gender binary are gaining the acceptance that all humans deserve. But the concept of “biological” sex identification remains a binary one. Although the traditional view of psychological gender has loosened, we still assume that a child is born, biologically, as a boy or girl. New research demonstrates that this assumption may be incorrect.

The general method for scientifically determining biological sex is through a karyotype, which is a picture of a person’s chromosomes. If an individual possesses a Y chromosome, it signifies a male with testes; if two X chromosomes are present instead, it signifies a female with ovaries. This is the same method that I was taught in my middle-school science classes. However, research has shown that this binary identification system can occasionally fail.

A karyotype is a picture of a person’s chromosomes, which form 23 pairs. The last pair determines the sex of the individual, depending on the presence of a Y. This is a typical male karyotype, with an XY pair. A typical female would show XX. (via intropsych)

For approximately the first five weeks of fetal development, the normal unborn baby lacks a specific set of male or female genitals. Between weeks 6 and 8, the regulation of certain genes controls whether a baby will develop testes or ovaries, and therefore be classified as a boy or girl. Specifically, an increase in expression of the SRY gene during this period leads to testes, while an increase in the expression of the WNT4 and RSP01 genes lead to ovaries. But regulatory processes are complex, and mutations in these genes can result in sexual characteristics incongruous with the strict two-sex system.

These atypical sexual characteristics are called Disorders of Sex Development (DSDs). For example, a case report from October of 2014 describes that during an inguinal hernia surgery on a 70 year old male, surgeons discovered that the man had ovaries. Despite his Y chromosome and his obviously male testes, the man had developed internal female sex organs. This irregular biological sex is known as 46,XY DSD, where gene mutation leads to female sex organs in a male. The same situation for a woman is known as 46,XX testicular DSD. These extreme cases are relatively rare (expressed in only 2 in 9000 people), but they may go unnoticed, and therefore our usual assumptions of internal sex organs based on external ones may sometimes be incorrect.

Furthermore, DSDs manifest in much more moderate cases. In the past two and a half decades, scientists have connected over 25 genes to the abnormalities that occur in sexual development. Subtle variations in some of these genes can result in biological characteristics that defy traditional categorization. In one case, an XX chromosome individual with a deficiency in the enzyme 21-hydroxylase can develop a condition known as congenital adrenal hyperplasia (CAH). A female with CAH has an enlarged clitoris and fused labia, which bear resemblance to a scrotum. On the other hand, a less severe deficiency of the enzyme results in milder symptoms, such as the excessive body hair usually reserved for males. Inclusive estimations claim that subtle DSDs may affect an entire one percent of the population.

Atypical cases create a grey zone for the normal sexual binary. And the wide possibility of variation in DSDs has led researchers to classify biological sex as a “spectrum” instead of two strict categories. This grey zone becomes even larger when we consider the case of “microchimaerism.” During pregnancy, the mother and fetus commonly exchange cells across the placenta, and these foreign cells can become incorporated into the body of the mother and child. This presence of foreign cells is called “microchimaerism,” and studies have shown that up to 63 percent of females who carried a son may have this condition. In studies involving mice, it has even been demonstrated that these foreign cells usually become incorporated into organs such as the brain. Therefore, a female can possess cells with a Y chromosome if she carried a son. Surely, the general method of “XY means male” and “XX means female” is by no means infallible.

A multitude of questions arises from this research. How do we determine biological sex? Should these conditions even be considered “disorders”, or does this language reveal our lack of understanding for the true workings of sexual characteristics? One extremely prevalent question is whether or not we should force these non-traditional individuals to conform to the current sex binary. In a world where you must be either biologically “male” or “female” to fit into society, many parents of children with DSD elect for surgery that establishes the child with one specific set of sexual organs. We may be robbing these individuals of their true biological sex, which we cannot yet accept as an option. As we continue to elucidate the complex processes of sexual development, we must keep our perspective in mind. Our ideas of a simple binary may alienate an entire group of individuals, just as we did for LGBTQ relationships. We ought not make the same mistake twice.

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