One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.

Dr. Eric Green, of the National Human Genome Research Institute's Genome Technology Branch, defines chromosome.

Related terms: autosome, birth defect, cell, deoxyribonucleic acid (DNA), gene, nucleus, protein, sex chromosome.