Genetic males have an X chromosome, so they have everything necessary to make ovaries. The issue is that the Y chromosome has the SRY gene [1], and that single

Genetic males have an X chromosome, so they have everything necessary to make ovaries. The issue is that the Y chromosome has the SRY gene [1], and that single gene is more or less responsible for kicking off the whole process of developing male genitalia in a fetus. That gene can get displaced off of the normal Y-chromosome and onto an X-chromosome resulting in XX Males [2] or XY Females [3]. Both conditions invariably result in sterility, though outwardly they appear mostly normal (XX Males externally look male, XY Females externally look female). That said, the fact that one gene seems to have so much effect suggests it's plausible that in the future we might be able to do something to make those individuals fertile, or to enable genital reconstruction surgeries for transgender people that enable new fertility. Note that much of this may be oversimplified, so any experts can feel free to apply some pedantry to the finer details. [1] https://en.wikipedia.org/wiki/Testis-determining_factor https://en.wikipedia.org/wiki/Testis-determining_factor [2] https://en.wikipedia.org/wiki/XX_male_syndrome https://en.wikipedia.org/wiki/XX_male_syndrome [3] https://en.wikipedia.org/wiki/XY_gonadal_dysgenesis https://en.wikipedia.org/wiki/XY_gonadal_dysgenesis