Muller's ratchet
A Ratchet in evolution. In asexual populations, every offspring carries all of its parent’s mutations. Without Recombination, there is no way to produce an offspring that is cleaner than the cleanest existing individual. So once the least-mutated lineage is lost to drift, that “best” genotype is gone forever—the ratchet clicks forward one notch. Over time, deleterious mutations accumulate irreversibly.
The mirror image of Clonal interference: the ratchet loses good genotypes because it can’t purge bad mutations; clonal interference loses good mutations because competing beneficial lineages can’t be combined.