Evolutionary expansion of DNA hypomethylation in the mammalian germline genome

Older and more conserved sperm HMRs are wider. (A) Mean sizes of promoter and nonpromoter HMRs in the seven-way orthologous genome of human and mouse sperm, grouped by estimated HMR emergence time in mammalian evolution. Error bars indicate standard errors of the mean. Significant Wilcoxon rank-sum test P-values are shown. The Boreoeutheria group contains HMRs conserved in all seven species, representing HMRs formed before and during the speciation of Boreoeutheria. Other groups represent HMRs formed during the speciation of respective lineages. (B) Distribution of HMR sizes in native genome assemblies, grouped by genomic context and conservation level.