BSIP VEM / SCIENCE PHOTO LIBRARY BSIP VEM / SCIENCE PHOTO LIBRARY
Down's Syndrome karyotype. Artwork based on a coloured light micrograph of the karyotype (full set of chromosomes) of a Down's syndrome female. Here, the 46 chromosomes are arranged in their 23 homologous pairs. Down's syndrome (trisomy-21) is caused by a chromosomal anomaly: the 21st set (blue, lower centre) has three rather than the normal two chromosomes. The defect results in mental retardation and physical disability, including a flattened face and an increased risk of infection and neck damage. The female sex chromosomes (both X-shaped) are at the bottom right corner. In a male, there would be one X and one Y chromosome.
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