Additionally, as adults they may be genetically of the opposite gender from that which they and their parents believe them to be. The difficulty in determining clear-cut specification of gender arises because there are at least three ways to define it. Two are biological and one is cultural. The first biological definition defines gender in terms of chromosomes. Males have an X and a Y chromosome.
Females have two X chromosomes.
The second biological definition assigns gender in terms of male and female genitalia. Americans generally want everyone to fit the third, cultural definition, even when people have biological characteristics that are not strictly in accord with a two-gender system. A second cause stems from the fact that all humans, no matter what their chromosomal makeup, have the biological capacity to develop either male or female genitalia and secondary sexual characteristics during pregnancy. Developmentally, some babies are born with male or female chromosomal makeup and with both male and female genitalia, or with some of the genitalia of the opposite chromosomal sex. Most intersexual Americans are unaware of their true biological gender because under current medical practice, physicians reassign the gender of intersexual infants at birth.