DR. P. BOYER / SCIENCE PHOTO LIBRARY DR. P. BOYER / SCIENCE PHOTO LIBRARY
False-colour light micrograph of normal human chromosomes, obtained by amniocentesis. Chromosomes are thread-like structures of the cell nucleus that carry genetic information in the form of genes. Each chromosome is seen to consist of two strands (chromatids) joined in a region known as the centromere or kinetochore. Chromosomes are capable of constructing exact copies of themselves whilst the cell is in the resting stage between successive divisions. When chromosome division occurs, the centromere splits longitudinally. The nucleus of every human cell contains 46 chromosomes, 23 of maternal and 23 of paternal origin.
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