Chromosomal information does not always align with an individual's gender identity

Q: Is XX always mean female and  XY always male?

Krishna: Things are not that easy to determine. Chromosomal information does not always align with an individual's gender identity.

The sex chromosomes (X and Y) are involved in determining whether a person develops male or female reproductive organs and characteristics. Typically, XX chromosomes lead to female development, and XY chromosomes lead to male development.

However some other things also play a role.

Gender Identity: Gender identity is a person's internal sense of self, which may or may not align with the sex they were assigned at birth. It's a spectrum, and individuals may identify as male, female, both, or neither, regardless of their chromosomes. 

Intersex Conditions: Some individuals are born with variations in their chromosomes or sex characteristics that don't fit neatly into male or female categories. This is known as intersex, and it highlights that biological sex is more complex than a simple binary. 

Hormonal and Brain Development: During prenatal development, hormones play a crucial role in shaping the brain and body, which can influence gender identity and sexual orientation. Variations in hormone exposure or brain development can contribute to gender incongruence. 

Social and Cultural Factors: Societal expectations and cultural norms also play a role in how individuals understand and express their gender. 

Examples of Mismatches:

Androgen Insensitivity Syndrome (AIS): Individuals with AIS have XY chromosomes but are resistant to male hormones, leading to female-like external genitalia despite having male internal reproductive organs. 

Congenital Adrenal Hyperplasia (CAH): Individuals with CAH have XX chromosomes but are exposed to high levels of male hormones before birth, leading to male-like external genitalia. 

Transgender Individuals: People who identify as transgender have a gender identity that differs from the sex they were assigned at birth, regardless of their chromosomes. 

A person can be a woman - a pregnant woman - and have XY chromosomes, and a person can be a man in all respects from birth and have XX chromosomes.

All mammal embryos start female and then some become male. Male development in therian mammals (that is, all mammals except the platypus and echidna) is triggered by a gene called SRY which is usually on the Y chromosome. But not always. You can have a Y chromosome with no SRY gene. You can have an X chromosome which has an SRY gene, or has a different gene which has mutated to act like an SRY.

There are various other factors, such as degree of tissue-response to androgens, masculinisation of a female embryo due to androgens produced by a male twin and duplication of chromosomes, which can result in an infant not conforming to the male=XY, female=XX pattern.

This is a page from a book by Biology Professor Emeritus, Ken Saladin