Infographic 10.1: Layers of Sexual Determination

Each of the four factors in the Venn diagram is shown as an oval, with text inside it. The ovals all meet at the center of the venn diagram in a cross shape, with an oval extending up, down, right, and left from the center. Each oval overlaps the two perpendicular to it, but not the one directly opposite to it, as follows. Secondary Sex Characteristics overlaps with Primary Sex characteristics and chromosomes, but not Gonads, Chromosomes overlaps with Secondary sex characteristics and gonads but not primary sex characteristics, Gonads overlaps with chromosomes and primary sex characteristics but not secondary sex characteristics, and primary sex characteristics overlaps with gonads and secondary sex characteristics but not chromosomes. There is text attached to each oval, explaining an exception. The ovals and exceptions read as follows. For Chromosomes: “One chromosome from each parent combines to determine genetic sex: XX (female) or XY (male).” Exception: Boys with Klinefelter’s syndrome (XXY) 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).” For Gonads: “Presence of Y chromosome causes gonads to become testes. If Y chromosome is not present, gonads develop into ovaries.” Exception: “Though genetically male and possessing testes, those with androgen-insensitivity syndrome do not respond to androgens and develop more femalelike sex organs and other characteristics.” For Primary Sex characteristics: “Testes secrete androgens that influence the development of male genitals. The absence of this signal leads to the development of female genitals.” Exception: “Intersexual development is apparent when individuals are born with sexual structures and organs that are ambiguous or inconsistent with genetic sex.” For secondary Sex characteristics: “Prompted by hormonal changes, these characteristics appear at puberty and are only indirectly involved with reproduction.” 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.” Text attached to the Secondary Sex characteristics and primary sex characteristics ovals explains that they are primarily influenced by hormones. Text attached to the Gonads and Chromosomes ovals explains that they are primarily influenced by genes.