Can’t live without two

We inherit two copies of each chromosome, one from our mothers and one from our fathers. Do we really need both of them? For some genes, one copy is sufficient, meaning that the organism can survive if one of the two copies is inactive or mutated. For other genes, the organism cannot survive without both copies. These genes are known as haploinsufficient and mutation or inactivation in just one of their copies leads to disease. We now have discovered that the cell possesses a special mechanism to ensure that both copies of haploinsufficient genes remain “switched on” at all times.