Mutation rate ($u$)

A mutation rate measures the frequency of mutation events per specified unit, such as per chromosome segment per generation. Its units and the population-size convention must be specified. If time is measured in $N$ generations and $\theta =2Nu$, each ancestral lineage has mutation intensity $Nu=\theta /2$ per unit of coalescent time.

An allele that increases the rate of mutations. In an asexual lineage it can hitchhike with a beneficial change, despite also increasing the production of harmful changes; genetic recombination can weaken that association.