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Genes are the basic units of heredity. Genes encode the information needed to make all the other parts of the cells that make up the human body. Chromosomes are the structures that carry the genes, like beads on a chain. Each person has 46 chromosomes, 44 autosomes and 2 of the sex chromosomes, the X and Y chromosomes. Females have 44 autosomes and 2 X chromosomes, while males also have 44 autosomes with one X and one Y chromosome. Twenty three of these chromosomes came from their mothers (i.e., 22 autosomes and one X chromosome) and 23 from their fathers (i.e., 22 autosomes and one that is either an X or a Y chromosome). Thus genes and the chromosomes that carry them occur in pairs – 22 autosome pairs and the 2 sex chromosomes.