Mouse duplicate genes are as essential as singletons

Duplicate genes in mouse are widely thought to have functional redundancy, and to be less essential than singleton genes. We analyzed nearly 3900 individually knocked out mouse genes and discovered that the proportion of essential genes is ∼55% in both singletons and duplicates. This suggests that mammalian duplicates rarely compensate for each other, and that the absence of phenotypes in mice deficient for a duplicate gene should not be automatically attributed to paralogous compensation.