At what stage in the life history of a mammal is the sex of an individual set?
Answer Details
The stage in the life history of a mammal at which the sex of an individual is set is "at conception" (as stated in).
The sex of a mammal, like other animals, is determined by the chromosomes inherited from its parents. Female mammals have two X chromosomes (XX), while male mammals have one X and one Y chromosome (XY). The sex of the individual is determined at the moment of fertilization, when the sperm from the male parent (which carries either an X or a Y chromosome) fuses with the egg from the female parent (which always carries an X chromosome) to form a zygote.
Therefore, the sex of an individual mammal is determined at conception, before birth or any other stages in the life history of the mammal. Puberty and adolescence are stages in the life history of a mammal where sexual characteristics become more apparent, but the sex of the individual has already been determined at conception.