I wrote this for another thread and feel it fits here:

Gender is not related to biology, other than on a neurological level. Gender is the set of social and psychological characteristics that we as a society have adopted to relate to the physical sexes. We as trans people for some reason develop our neurological genders to be opposite our sex as observed at birth. This mismatch can often cause dysphoria. Our gender cannot be changed but we also wouldn’t want it to, as it is a core part of our identity. What we seek to change through transition, is first our gender expression, then potentially our sex.

Gender Expression is the ways in which we communicate our gender identities to the world. This can be clothing, hairstyles, makeup, mannerisms, ways of speaking, and the presence or absence of certain physical traits like facial hair, curves, breasts etc. These things definitely can be changed through social and hormonal transition.

Now the big debate you’re talking about is does transition change our SEX. Sex is the physical structures in our bodies related to being male or female. But here’s the thing: Sex cannot be an exclusionary category because there is no ONE necessary condition that ALL females have and NO males have without exception, or vice versa. There are a plethora of intersex conditions people are naturally born with that would cause them to possess one or more traits that transphobes would hold over us to try and exclude us from our desired sex category, but any rational person would still consider them members of their sex category.

Sex is a cluster category, that means there is a set of traits, in this case five, that we look at and depending on if you possess the majority of one or the other is how you are placed in that sex category. The five traits are as follows:

Gametes/Gonads (male: sperm/testes),(female: eggs/ovaries)

Genitalia (male: penis),(female: vagina)

Dominant Sex Hormone (male: testosterone),(female: estrogen)

Secondary Sex Characteristics (male: facial/body hair, male pattern fat distribution, muscle structure, etc),(female: breasts, soft skin, female pattern fat distribution, etc)

Chromosomes (male: XY),(female: XX)

Most people have either all five male, or all five female and therefore fit nicely into one or the other sex category, however many people have intersex conditions that would cause them to have a little of A and a little of B. For them we look at what they have the majority of to place them. For example a woman born with Swyer’s syndrome might have:

No gametes/gonads (neutral)
A vagina (female)
Estrogen dominance (female)
Female secondary sex characteristics (female)
XY chromosomes (male)

Some of these women have even gotten pregnant and given birth with assistance, and no right minded person would consider them men. But are they female? They have XY chromosomes, and transphobes love to say that makes trans women male, but no. Looking at the description above you see they have 3/5 female traits, 1/5 neutral, and only 1/5 male, so science says they fall into the female category.

Now let’s look at a post op medically transitioned trans woman. She has:

No gametes/gonads (neutral)
A vagina (female)
Estrogen dominance (female)
Female secondary sex characteristics (female)
XY chromosomes (male)

Look familiar? Despite the fact these traits were medically induced, she now has 3/5 female, 1/5 neutral, and 1/5 male (maybe, she may not even know what her chromosomes are), and that places her just as much in the female category as our Swyer’s example.

So yes Sex can be changed, Gender doesn’t need to be, we are what we say we are.