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Down syndrome is the most common autosomal syndrome in man. The incidence of trisomy 21
due to translocation is about 3.5-5%. Translocations are usually centric fusions between a 21 and a
D group (54.2%) or a G group (40.9%) chromosome. Since the short arm of 21 carries no phenotypically
active genes, even if the short arm of 21 is lost, usually there is... |