Every time a cell divides, the telomeres capping its chromosomes lose roughly 50 to 200 base pairs, and once they are nearly gone the cell stops dividing altogether: the Hayflick limit. Two metres of DNA thread only fit inside the nucleus through successive rounds of condensation, wound around nucleosomes and coiled again into the familiar X shape at division. Aneuploidy means a chromosome too many or too few, such as a 47-chromosome karyotype with three copies of chromosome 21, while telomerase rebuilds the caps, which is why cancer cells keep dividing without end.
Every time a cell divides, the telomeres capping its chromosomes lose roughly 50 to 200 base pairs, and once they are nearly gone the cell stops dividing altogether: the Hayflick limit. Two metres of DNA thread only fit inside the nucleus through successive rounds of condensation, wound around nucleosomes and coiled again into the familiar X shape at division. Aneuploidy means a chromosome too many or too few, such as a 47-chromosome karyotype with three copies of chromosome 21, while telomerase rebuilds the caps, which is why cancer cells keep dividing without end.
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