- A Determined mainly by the ambient environmental temperature present specifically during early embryonic development, much like in certain reptile species studied widely
- B Determined by sex chromosomes: XX = female, XY = male. Y chromosome carries SRY gene, which triggers testicular development; without it, female development occurs by default
- C Determined by the total overall number of autosomes present within the individual's complete karyotype overall, rather than by the sex chromosomes themselves in any way
- D Determined mainly by the biological age of the mother at the precise moment of conception itself, rather than by any underlying genetic factor present at the time
Correct answer: B. Determined by sex chromosomes: XX = female, XY = male. Y chromosome carries SRY gene, which triggers testicular development; without it, female development occurs by default
Explanation: Sex determination in humans is chromosomal (Henking, 1891; McClung, 1902). SRY on Y chromosome triggers testes. Testes produce testosterone (via 5alpha-reductase converted to DHT which masculinizes external genitalia), AMH (Mullerian inhibiting factor, causes regression of Mullerian ducts). Without SRY: ovaries; without testosterone: female genitalia develops. Phenotypic sex can differ from chromosomal sex in disorders of sexual development (DSD).
Concept context
Male and female reproductive systems, gametogenesis, fertilization, implantation, pregnancy, and reproductive health.