A mutation accumulation (MA) experiment is a genetic experiment in which isolated and inbred lines of organisms (so-called MA lines) are maintained such that the effect of natural selection is minimized, with the aim of quantitatively estimating the rates at which spontaneous mutations (mutations not caused by exogenous mutagens) occur in the studied organism. Spontaneous mutation rates may be directly estimated using molecular techniques such as DNA sequencing, or indirectly estimated using phenotypic assays (observing how an organism’s phenotype changes as mutations accumulate).