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Human chromosomes. Coloured scanning electron micrograph (SEM) of human chromosomes prepared with the harlequin staining technique. Chromosomes are a packaged form of a cell's genetic material DNA (deoxyribonucleic acid). The DNA condenses into chromosomes during cell replication. Each chromosome consists of two identical strands (chromatids), aligned parallel to each other and joined at an area called the centromere. The staining shows the formation sequence, with the second chromatid (white) of each pair formed as a direct copy of the first chromatid (purple). Structural changes are also seen.
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