A normal human body cell contains 46 chromosomes, arranged in 23 pairs.
One chromosome in each pair usually comes from the mother and the other from the father. The first 22 pairs are autosomes, while the 23rd pair consists of sex chromosomes. Most females have XX and most males have XY, although variations in sex-chromosome number also occur.
Human egg and sperm cells are different: they are haploid and contain 23 chromosomes rather than 46. Fertilisation combines one set from each parent, restoring the diploid number in the resulting embryo.
The chromosome count is not a measure of biological complexity. For example, some plants and animals have many more chromosomes than humans. A change in chromosome number, such as an extra chromosome 21, can affect development and cause a genetic condition such as Down syndrome.