Final answer:
Human biological sex is determined by the combination of sex chromosomes inherited from the parents: females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). Option A) X and Y chromosomes is the correct answer to the question.
Step-by-step explanation:
The sex of humans is determined by the chromosomes an individual inherits. Sex chromosomes play a critical role in this determination. In humans, there are two types of sex chromosomes, X and Y. Females typically have a homologous pair of X chromosomes (XX), while males have one X chromosome and one Y chromosome (XY).
The presence of the Y chromosome is what leads to the development of male characteristics. If only X chromosomes are present, no Y chromosome is there to trigger development into a male; therefore, the embryo develops female characteristics. Thus, the correct answer to how sex is determined in humans is A) X and Y chromosomes.
Note that this system is specific to mammals, including humans. In other species, such as birds, sex determination involves different chromosomes, namely Z and W, but that is not the case in humans.