Biological Sex Glossary

Biological sex is made up of many different components, and people have tried to categorize it into two groups (female and male) for a long time. There are generally two ways of grouping people: by external features (more appropriately understood as gender expression rather than biological sex) and by biological markers. We will focus on a more in-depth understanding of biological markers here, as the range and variance of gender expression as reaching beyond two rigid options is generally well enough understood.

Most people are taught from an early age that there are two sexes: female (with two X chromosomes, higher levels of estrogen and progesterone, a uterus, vagina, clitoris, breasts, and wide hips) and male (with one X and one Y chromosome, androgens, testosterone, a penis, testicles, scrotum, low voice, and facial hair). These assumptions about the characteristics and biology of the sexes will be familiar to almost everyone.

Assumptions about a person’s biology are not, however, able to be known or even guessed just by looking at a person.

Let’s begin breaking out of the binary assumption of gender by look at the biological categories, or markers, that people use when they are discussing sex. These characteristics can be placed in two general categories: Primary Sexual Characteristics (PSC) and Secondary Sexual Characteristics (SSC). PSC include parts of the body directly related to reproduction. SSC include non-reproductive biologically related differences between females and males. (See the tables below for details.)

When discussing secondary sexual characteristics, many people understand intuitively how there is a range of possibilities rather than merely two possibilities. For example, though men are, on average, taller than women, there are some women who are taller than some men. Similarly, some woman have very little breast tissue, while some men have quite a lot.

It is when discussing primary sexual characteristics that many people are less certain about the existence of a range rather than merely two options. When a person’s primary sexual characteristics do not fall under the categories of female or male, they are Intersex. Intersex can mean a wide range of things for different people. For example, someone might have XX chromosomes, but their clitoris is enlarged and looks more like a small penis. (For more information, visit the InterACT Advocates for Intersex Youth)

It is clear, given the biological evidence, that biological sex is a range in the same ways that gender identity and expression are ranges. However, most people in the United States are less aware of the potential range of biological sex. Keeping this information in mind will help you support participants’ understanding of themselves and other people. The following table goes into some depth describing the many variations that are possible. Keep in mind science is ever evolving and this table may not include every possible variation.

Term Chromosomes Hormones Gonads External Internal
Typically Female XX Higher levels of estrogen and progesterone Ovaries Clitoris (glans, hood), labia (inner, outer, and frenulum), vulva Bartholin's glands, cervix, clitoris (frenulum), fallopian tubes, skene's gland, uterus, vagina
Typically Male XY Higher levels of androgens, such as testosterone Testicles Penis (foreskin, frenulum, and glans), scrotum Bulbourethral glands, epididymis, prostate, seminal vesicles, vas deferens
Swyer Syndrome XY Lower levels of estrogen and progesterone than the typical female Gonadal streaks Clitoris (glans, hood), labia (inner, outer, and frenulum), vulva Bartholin's glands, cervix, clitoris (frenulum), fallopian tubes, skene's gland, uterus, vagina
Turner Syndrome X Lower levels of estrogen and progesterone than the typical female Ovaries Clitoris (glans, hood), labia (inner, outer, and frenulum), vulva Bartholin's glands, cervix, clitoris (frenulum), fallopian tubes, skene's gland, uterus, vagina
Mayer Rokitansky Kuster Hauser Syndrome (MRKH) XX Similar levels of hormones to a typical female Ovaries Clitoris (glans, hood), labia (inner, outer, and frenulum), vulva Varies, though the clitoris (frenulum) and fallopian tubes are usually present. Uterus and vagina are often smaller than the typical female’s, or absent.
Progestin Induced Virilization XX Similar levels of hormones to a typical female Ovaries Varies significantly. May resemble the external genitalia of the typical female, the typical male, or a combination of the two. Varies. The uterus and fallopian tubes will develop, but the vagina and the cervix may or may not develop.
Complete Androgen Insensitivity Syndrome (CAIS) While individuals with XX or XY chromosomes can have CAIS, it is only considered an intersex condition in people with XY chromosomes. Cannot respond to androgens Testicles Clitoris (glans, hood), labia (inner, outer, and frenulum), scrotum, vulva Clitoris (frenulum), vagina
Congenital Adrenal Hyperplasia (CAH) While individuals with XX or XY chromosomes can have CAH, it is only considered an intersex condition in people with XX chromosomes. Extremely high production of androgens Testicles Varies. May highly resemble typical female external genitalia, though it is common for the clitoris to be larger and for the labia to resemble the scrotum Bartholin's glands, cervix, clitoris (frenulum), fallopian tubes, skene's gland, uterus, vagina
Klinefelter Syndrome XXY Lower levels of androgens than the typical male Testicles Penis (foreskin, frenulum, and glans), scrotum Bulbourethral glands, epididymis, prostate, seminal vesicles, vas deferens
Partial Androgen Insensitivity Syndrome (PAIS) While individuals with XX or XY chromosomes can have PAIS, it is only considered an intersex condition in people with XY chromosomes. Variable ability to respond to androgens Testicles Varies significantly. May resemble the external genitalia of the typical female, the typical male, or a combination of the two. Varies significantly. May include partially developed genitalia associated with both typical female and male development.
Mosaicism X/XX, XY/XXY, etc. While most individuals have the same chromosomes in all of their cells, individuals with sex chromosome mosaicism have different sex chromosomes in different cells. For example, someone with Mosaic Turner Syndrome will have just one X chromosome in some cells and two X chromosomes in others. Varies by condition Varies by condition Varies by condition Varies by condition