Chromosomes
Chromosomes are the thread-like ‘packages’ of DNA in the nucleus of a cell. Humans have 23 pairs of chromosomes, 46 in all. 44 of these are very similar to each other. The other two are the sex chromosomes; they are called XX in females, and are also similar to each other. In males the sex chromosomes are called XY and they are very different from each other. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.
