A human cell's nucleus has 23 pairs of chromosomes for a total of 46.
The first 22 pairs of chromosomes are known as autosomes. These are homologous chromosomes, which means that their chromosomal sides have the same genes (DNA sections) in a similar sequence.
Allosomes are the 23rd pair of chromosomes, which have two X chromosomes in most females and one X chromosome and one Y chromosome in most males. Females have 23 pairs of homologous chromosomes but males have 22 pairs homologous chromosomes.