Most people have 23 pairs of chromosomes, half of each pair coming from each parent. Among the chromosomes people inherit from their parents are two sex chromosomes, known as X and Y.
All males receive the X chromosome from their mother and the Y chromosome from their father. The Y chromosome has specific genes that will develop the male reproductive body parts: penis, testes and scrotum.
Females have two X chromosomes, one inherited from each parent. Female reproductive body parts (clitoris, vagina and labia) will form if there is no Y chromosome present.
Sex hormones are needed for male and female reproductive body parts to develop, both before birth and during puberty. Sex hormones are “chemical messengers” made by sex glands in the body. Genetic factors (for example, if a Y chromosome is present or not) are important for sex glands to develop male or female.
Males typically have sex glands known as testicles, which make male hormones (testosterone).
Females typically have sex glands known as ovaries, which make female hormones (estrogen).