Most human cells contain 46 chromosomes arranged in 23 pairs. Twenty-two pairs are autosomes (non-sex chromosomes), and the 23rd pair consists of sex chromosomes—XX in females and XY in males. Each chromosome is made up of DNA and proteins, and we inherit one chromosome from each pair from our mother and one from our father.
However, not all cells contain the full complement of 46 chromosomes. Red blood cells lack a nucleus entirely and therefore have no chromosomes. Reproductive cells—sperm and egg cells—contain only 23 chromosomes (one from each pair), which is half the typical number. When a sperm and egg fuse during fertilization, their chromosomes combine to restore the full 46 in the resulting embryo.
Additionally, mitochondria, the cell's energy-producing structures, contain their own small circular DNA molecules called mitochondrial DNA, though these are not typically counted among the 46 main chromosomes when discussing human chromosome numbers. In rare cases, some individuals have different chromosome numbers due to genetic conditions like Down syndrome (47 chromosomes) or Turner syndrome (45 chromosomes), but 46 is the standard for typical human development.