A normal human somatic cell contains 46 chromosomes.
These 46 chromosomes are arranged in 23 pairs: 22 pairs of autosomes and one pair of sex chromosomes. Somatic cells are the body's non-reproductive cells, including most cells in organs and tissues. Because they contain two chromosome sets, they are called diploid cells.
Human egg and sperm cells normally contain 23 chromosomes, one chromosome from each pair. At fertilization, the egg and sperm combine to restore the usual total of 46 chromosomes in the resulting cell. This distinction explains why 23 and 46 are both important numbers in human genetics.
Chromosome number alone does not describe every genetic condition. For example, Down syndrome usually involves an extra copy of chromosome 21, producing 47 chromosomes in many or all cells. Mature red blood cells are a notable exception to the usual somatic-cell pattern because they lose their nucleus and chromosomes during development.