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How many chromosomes?
People with Down’s syndrome have 47 chromosomes, rather than the usual 46. They have an extra copy of chromosome 21, the smallest chromosome. Scientists can use a technique sometimes called 'chromosome painting' to diagnosis this condition. It uses a special type of fluorescing probe, which lights up all the chromosome 21s.
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Chromosome painting lights up the extra chromosome 21 in the cells of people with Down syndrome (pink and light blue dots).
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