Intersex is a set of medical conditions that feature congenital anomaly of the reproductive and sexual system.
Transgender people are those whose psychological self differs from the social expectations for the physical sex they were born with.
Gender Equity Resource Center
What does sex and gender mean for transgender people?
Transgender is an “umbrella term for people whose gender identity, expression or behavior is different from those typically associated with their assigned sex at birth.” Transgender people include “transsexuals, cross-dressers (transvestites), transgenderists, gender queers, and people who identify as neither female nor male and/or as neither a man or as a woman.”
Trans men = transitioned or transitioning adult human female, female-to-male (FTM), female-to-trans (FtT)
Female = XX sex chromosomes that determine female genitalia (vagina, ovaries), female secondary characteristics (breasts, etc.), etc.
In summary, trans men = XX or female, AKA biologically women
Trans women = transitioned/transitioning adult human male, male-to-female (MTF), male-to-trans (MtT)
Male = XY sex chromosomes that determine male genitalia (penis, testes), male secondary characteristics (beard, etc.), etc.
In summary, trans women = XY or male, AKA biologically men
What about intersex people?
Intersex does not mean trans (not transgender men or women, not transsexual). Intersex refers to disorders of sex development in which external sex (genitals) does not match internal sex (ovaries, testes).
46, XX Intersex = female, XX sex chromosomes, external genitalia appears male, internal sex (ovaries) is normal
46, XY Intersex = male, XY sex chromosomes, external genitalia may be female, internal sex (testes) may be normal, malformed or absent
True Gonadal Intersex = both internal sex tissue (ovarian and testicular), XX, XY or both sex chromosomes, external genitals may be ambiguous or appear either male or female
Complex or Undetermined Intersex = missing or extra sex chromosomes, including XO, XXX, XXY, no discrepancy between internal and external sex, but problems with sex hormone levels or overall sexual development may be present
According to the British Medical Journal, “The overall incidence of all disorders of sexual development (DSD) has been estimated at 1.7%, but this includes conditions that do not present with ambiguous genitalia at birth, such as Turner’s syndrome, Klinefelter’s syndrome, and complete androgen resistance.” As such, it is currently debated whether or not this number is representative.
The Intersex Society of North America notes that “If you ask experts at medical centers how often a child is born so noticeably atypical in terms of genitalia that a specialist in sex differentiation is called in, the number comes out to about 1 in 1500 to 1 in 2000 births.” This translates to a prevalence of about 0.05-0.067%.
The term intersex would not exist without the distinct concepts of female and male and does not disprove sexual dimorphism or the sex binary. It is simply the rare exception to the general rule.