This map also showed that while women are responsible for most recombination, men generate the bulk of "de novo" mutations. In a much discussed paper from 2012 they demonstrated that the number of such mutations — variants that appear in the genomes of children but are not inherited from either parent — increases with paternal age and constitute a major source of rare diseases of childhood.  A detailed analysis of the different types and distribution of maternal and paternal "de novo" mutations was published in 2017, and a subsequent paper demonstrated how "de novo" mutations in parents can be passed on.  