Final answer:
In humans, the sex of the offspring is determined by the sex chromosomes. Females have XX chromosomes, and males have XY chromosomes. The father's sperm, carrying either an X or Y chromosome, determines the sex of the child.
Step-by-step explanation:
In humans, the sex of the offspring is ordinarily determined by the sex chromosomes. Specifically, sex is determined by the presence of XX chromosomes (homozygous) in females and XY chromosomes (heterozygous) in males. During reproduction, mothers pass only X chromosomes to their children, while fathers pass either an X or a Y chromosome. If the child inherits an X chromosome from both parents, the child will be female, with an XX pairing. However, if the child inherits an X chromosome from the mother and a Y chromosome from the father, the child's sex will be male, with an XY pairing. Hence, the father's sperm ultimately determines the sex of the child since it can carry either the X or Y chromosome, leading to a 50:50 chance for the child to be either male or female.