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"Chromosomes, computer artwork. Chromosomes, which consist of two identical chromatids joined at a centromere, are composed of deoxyribonucleic acid (DNA) coiled around proteins. There are 46 chromosomes in most cell nuclei in a human body; 22 pairs and a gender-determining pair. DNA contains sections, called genes, that encode the body's genetic information, determining each cell's structure, function and behaviour." (KEYSTONE/SCIENCE PHOTO LIBRARY/EQUINOX GRAPHICS)