Traditionally, of course, scientists couldn't take a yardstick to the DNA-containing chromosomes contained in human cells and measure the distance between genes.

FORBES: DeCode's Genetic Breakthrough Barely Registers

Some have XX chromosomes in some cells of their body and XY in others those rare, true hermaphrodites.

FORBES: Is Sex Reassignment Surgery a Basic Human Right?

This happens during the production of sex cells, and its effect is to halve the number of chromosomes in a cell (the number returns to normal when two sex cells combine during fertilisation).

ECONOMIST: Genetic engineering

Egli is among the handful of scientists who have been working to perfect the technique with human cells and in 2011, succeeded in producing human stem cells, but with double the number of chromosomes.

CNN: SHARE THIS