A chromosome is an organized package of DNA found in the nucleus of the cell. Different organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes--22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosomes, X and Y. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.


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A chromosome is the structure housing DNA in a cell. Chromosomes are structurally quite sophisticated, containing elements necessary for processes such as replication and segregation. Each species has a characteristic set of chromosomes with respect to number and organization. For example, humans have 23 pairs of chromosomes--22 pairs of numbered chromosomes called autosomes, 1 through 22, and one pair of sex chromosomes, X and Y. Each parent contributes one chromosome of each pair to an offspring.

- Eric D. Green, M.D., Ph.D.

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