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Identifying chromosomes

Of the 23 pairs of human chromosomes, two are the sex chromosomes: X and Y, named because of their shapes. The remaining 22 pairs are numbered in decreasing order of size, 1 being the largest. The smallest chromosome is actually chromosome 21 not 22, due to a mistake in the original numbering system. Once scientists have photographed chromosomes under the microscope, they can arrange them into their pairs to get a person's karyotype, or 'chromosome profile'.

Chromosomes from a male, with one X- and one Y-chromosome. A female has two X-chromosomes.
Chromosomes from a male, with one X- and one Y-chromosome. A female has two X-chromosomes.
Applied Imaging Corporation

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