A germline mutation (error in replication of DNA) occurs every 1 Mbp per generation. Cross species comparisons suggest there are approximately 4 coding mutations per genome per generation, one third of which will be deleterious.
Mutation gives rise to 0.8 polymorphic sites per 1000 base pairs in human populations: a polymorphism is a location (locus) in the sequence where 1% or more of individuals carry a nucleotide different from the rest of the population. Alleles are the different variants at the locus.