Sex (the fusion of two gametes to produce a new individual) is a *mechanism*, and so it makes perfect sense to define one’s sex in terms of machinery: what machinery (reproductive anatomy) does one develop to support either small or large gametes.

Even if the machinery is not presently functional, the machinery still has a function, which evolved to support the production and release of either small or large gametes.

This is how we recognize sex across all anisogamic species: through what gamete machinery one develops.

And because there are only two gamete types, there are therefore only two distinct gamete machineries.

Chromosomes are the blueprints that encode the development of the specific gamete machinery.

And so, the machinery that develops is contingent upon the blueprints given.

Thus, the phenotype of the fetus is the result of the development path it followed based on the genetics.

Mess around with the blueprints (translocation of SRY to XX, or removal of the ovarian transcription factor FOXL2) and you’ll get the specific gamete machinery based on that new code.

XX+SRY often results in small gamete machinery (male), for example.