How does sex differentiation occur in biological organisms?

Sex differentiation in biological organisms occurs through a combination of genetic and hormonal factors. The presence of specific sex chromosomes, such as XX for females and XY for males in humans, determines the individual's sex. Hormones, such as testosterone and estrogen, play a crucial role in the development of secondary sexual characteristics, such as reproductive organs and physical traits. During embryonic development, the expression of certain genes and the influence of hormones guide the differentiation of gonads into testes or ovaries, leading to the development of male or female characteristics.