EVEN apparently normal people can have dramatically different numbers of genes. This has taken geneticists by surprise, and they are still puzzling over exactly what it means. But it is likely to change our understanding of how differences in the genome lead to differences between one person and the next.
Too many or too few copies of a gene are traditionally considered to be hallmarks of inherited conditions such as Down’s syndrome or of diseases such as cancer. DNA differences between healthy people were thought to be largely limited to subtle, scattered alterations in the genome.
But a team led…
