Can Human Body Cells Ever Have More Than 46 Chromosomes?

Yes, this is possible but it does lead to problems. About 1 in every 1000 person born in the UK has an extra copy of chromosome 21 in all their body cells, so that they have 47 chromosomes rather than the usual complement of 46.

The possession of an extra copy of chromosome 21 causes Down's syndrome and people with this syndrome usually battle with mental and physical disabilities.

The reason for the extra chromosome is usually a failure of the chromosome 21 to break apart properly during the phase of cell division when the chromosomes are copied. Two cells result, one with the extra copy and one with no copy of chromosome 21 at all. If this gamete combines with a normal one from the other parent, the fertilised egg is not viable - it does not have the capacity to develop into an embryo.

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