Neil’s research lab in London is full of female scientists. This is not surprising given his interest in female sex chromosomes and what is responsible for causing them to switch off. Every human female has silenced one of each  X chromosome that she got from her parents. This results in a mosaic pattern (those cells with dads X switched on have mum's switched off and vice-versa). This is common to all female mammals, and the resulting variation goes beyond that contained within our DNA alone. Neil has helped to discover a gene called Xist (exist), which makes a molecule similar to DNA that sticks to the X chromosome, physically blocking gene activity.