What is the karyotype found in Down syndrome?
Down syndrome is an aneuploidy, i.e., a numeric alteration of chromosomes within the cells compared to the normal number of chromosomes of the species. Affected individuals have in their cells an additional chromosome 21 instead of only one pair. For this reason the condition is also called trisomy 21. The affected person has karyotype with 47 chromosomes: 45 + XY or 45 + XX.
