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Clonal interference is a phenomenon in the population genetics of organisms with significant linkage disequilibrium, especially asexually reproducing organisms. It occurs when two (or more) different beneficial mutations arise independently in different individuals. Prior to, or in the absence of genetic recombination, the mutations cannot be combined into a single more-fit genotype, but instead compete against each other. This typically leads to the loss of one of them, confirming that the fate of an advantageous mutation can be determined by other mutations present in the same population. In organisms with sexual reproduction, two beneficial mutations arising in different organisms can be combined in a descendant. This allows evolution to proceed more rapidly, a phenomenon known as the Hill-Robertson effect.
Clonal interference is named because an asexual lineage ("clone") with a beneficial mutation, which would likely be fixed if it occurred alone, may fail to be fixed, or even be lost, if another beneficial-mutation lineage arises in the same population; the multiple clones interfere with each other. This can also occur in cancer and pre-cancer cell lineages within a patient .