Oct 1

Rev Gav

Biological Sex

Biological Sex is non-binary and complex and you cannot base someone’s Biological sex solely on outward appearance.

A mixture of fruits whole and halved showing their interiors. pomegranate, banana, lemon, and grapes.

I wanted to understand the complexity of biological sex but make it simple to understand (I’m not a biologist!). I understand that we have biological sex, sexuality, and gender, but this short article is only about biological sex. It is important to note that a person’s biological sex may influence their sexuality and/or gender but does not prescribe it!

The following is adapted from a post by Rebecca Helm, a biologist and an assistant professor at the University of North Carolina, Asheville.

AMAB and AFAB

Children are Assigned Male at Birth (AMAB) or Assigned Female at Birth (AFAB) based on their outward physical appearance (and sometimes hormone levels).

Sometimes an assignment of ‘intersex’ is made when the person is ‘physically’ in appearance intersex, but importantly, the term intersex does not just apply to outward appearance but can be based on chromosomes, genes, hormones, and/or cells.

Although 1 in 1000-4500 children are born with a visible difference in sexual development, it is estimated that 1%-2% of the world’s population are intersex.

Note: For some, the phrase ‘difference in sexual development’ is preferred to ‘intersex’. e.g. in the paediatric evaluation of an infant with atypical genital appearance.

Chromosomal Sex

A chromosome is a package of genes. Typically, a person has 46 chromosomes in each cell, divided into 23 pairs, which includes two sex chromosomes. Half the chromosomes are inherited from the father and the other half from the mother. The chromosomes contain genes, which determine an individual’s characteristics, such as eye colour and height.

Chromosomal sex is caused by two chromosomes, X and Y where a female has XX chromosomes and a male has XY chromosomes.

However, sometimes a male may be born with an extra X chromosome making them XXY. This is called Klinefelter syndrome. This chromosome carries extra copies of genes which can affect the person mentally and physically. It may also interfere with the development of the testicles and mean the person produces less testosterone (male sex hormone) than usual.

Sometimes a male may be born with an extra Y chromosome making them XYY. This is called Jacob’s syndrome and this can affect a person’s mental function and physical growth.

Sometimes a male may be born with an extra X and an extra Y chromosome making them XXYY. Again this can affect a person both mentally and physically. Adolescents and adults with this condition usually have small testes that do not produce enough testosterone, which is the hormone that directs male sexual development.

Sometimes a female (XX) may have one copy of the X chromosome missing (XO) or altered. This is called Turner syndrome and commonly leads to short stature, reduced functioning of the ovaries, and reduced female sex hormones.

To make things even more complicated, some people have a mix of cells, some of which are XX and some of which are XY although this is rare.

Genetic Sex

There is one gene on the Y chromosome that determines sex and it is called the SRY gene. During human embryonic development the SRY protein turns on male-associated genes. Having the SRY gene on the Y chromosome makes you ‘genetically’ male.

Sometimes the SRY gene is missing on the Y chromosome or is out of place and on the X chromosome.

A person with a Y chromosome with no SRY means that genetically they are female and may physically present as female, but chromosomally they are male (XY).

A person with an X chromosome with an SRY means they are genetically male and may physically present as male but are chromosomally female (XX).

Hormonal Sex

Sex-related genes turn on hormones in specific areas on the body and the reception of those hormones by cells throughout the body.

A ‘hormonal male’ produces normal levels of male-associated hormones and a ‘hormonal female’ produces normal levels of female-associated hormones.

Sometimes females have higher levels of ‘male’ hormones than some males leading to male physical characteristics.

Sometimes males have higher levels of female hormones than some females leading to female physical characteristics.

A developing body may not produce enough hormones for their genetic sex.

It is possible for a person to be genetically male or female, chromosomally male or female, and hormonally (physically) non-binary.

Cellular Sex

Cells have receptors that ‘hear’ the signal from sex hormones, however, sometimes those receptors do not work and despite the correct amount of hormones being produced for their genetic sex, their bodies can again, be non-binary.

It is possible for a person to be genetically male or female, chromosomally male or female, hormonally (physically) non-binary, and/or cellularly (physically) non-binary.

Summary

Biological Sex is non-binary and complex. Even within what has been written above there is great variation. You cannot have a binary classification system with more than two configurations even if two of those configurations are more common than others, therefore you cannot base someone’s Biological sex solely on outward appearance.