Our chromosomes are like socks: you want to have a pair of them, nothing more and nothing less. We have 23 pairs of chromosomes per cell, and there are great costs to exceeding this ideal number. Having odd numbers of certain chromosomes leads to genetic disorders like Down syndrome, while babies with three of every chromosome – triploids – tend to be lost to miscarriage or die within months. But having extra chromosomes isn’t always bad. In our liver, it’s positively encouraged.

Cells with extra chromosomes are known as polyploids and they’re a common feature in all mammalian livers. Some have four copies of each chromosome; others have eight, even sixteen. Now, Andrew Duncan from the Oregon Health and Science