An introductory text reads, When thinking about the biological factors that determine sex, most people envision the primary sex characteristics that indicate our assignment at birth. But one’s sex is made up of many layers with different influences. Though they often all combine in a predictable way, there can be exceptions at any point. Looking at variations at each layer demonstrates the complex reality of sex that goes far beyond what is declared on our birth certificates.
Four overlapping ovals are labeled as follows:
The first oval is labeled Chromosomes. An accompanying text reads, one chromosome from each parent combines to determine genetic sex: X X (female) or X Y (male). A callout reads, exceptions: Boys with Klinefelter’s syndrome (X X Y) develop normally until puberty, but can have underdeveloped male characteristics or additional female secondary sex characteristics because of the extra X chromosome. Also: Turner’s syndrome (female born with an absent or incomplete X chromosome).
The second oval is labeled Gonads. Accompanying text reads, Presence of Y chromosome causes gonads to become testes. If Y chromosome is not present, gonads develop into ovaries. A callout reads, exception: Though genetically male and possessing testes, those with androgen-insensitivity syndrome do not respond to androgens and develop more female-like sex organs and other characteristics.
The third oval is labeled Primary sex characteristics. Accompanying text reads Testes secrete androgens that influence the development of male genitals. The absence of this signal leads to the development of female genitals. The callout reads, intersexual development is apparent when individuals are born with sexual structures and organs that are ambiguous or inconsistent with genetic sex.
The fourth oval is labeled Secondary sex characteristics. Accompanying text reads, Prompted by hormonal changes, these characteristics appear at puberty and are only indirectly involved with reproduction. A callout reads, exception: Those with 5-alpha reductase deficiency appear female at birth. At puberty, hormonal surges cause external masculinization sufficient to make them indistinguishable from other men.
Chromosomes and Gonads are primarily related to genes. Primary and secondary sex characteristics are primarily influenced by hormones.