In mammals, what are the sex chromosome configurations for female and male individuals?

• A. Female: XX; Male: XY.
• B. Female: ZX; Male: ZZ.
• C. Female: ZZ; Male: ZX.
• D. Female: XY; Male: YY.

Answer: (A)

Sex in mammals is determined by the combination of sex chromosomes inherited from the parents. Females have two X chromosomes, while males have one X and one Y. The Y chromosome carries the SRY gene that directs male development; without a Y, development proceeds along the female pathway with two X chromosomes. Inheritance means every offspring receives an X from the mother, and the father can contribute either an X (giving XX, a female) or a Y (giving XY, a male). So the standard mammalian configurations are XX for females and XY for males. The other chromosome setups listed pertain to different species and don’t apply to mammals.