 In summary, male mutation bias primarily is due to replication-dependent mutations occurred in the male germline more than in the female germline, but replication-independent mutations also contribute to alleviating the difference.A GC-AT bias is a bias with a net effect on GC content.For instance, if G and C sites are simply more mutable than A and T sites, other things being equal, this would result in a net downward pressure on GC content.