population genetics Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as Adaptation (biology), adaptation, s ...

, the Hill–Robertson effect, or Hill–Robertson interference, is a phenomenon first identified by Bill Hill and Alan Robertson in 1966. It provides an explanation as to why there may be an evolutionary advantage to

genetic recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryot ...

Explanation

In a population of finite but effective size which is subject to

natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the Heredity, heritable traits characteristic of a population over generation ...

, varying extents of linkage disequilibria (LD) will occur. These can be caused by

genetic drift Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...

or by

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

, and they will tend to slow down the process of

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

by natural selection. This is most easily seen by considering the case of disequilibria caused by mutation: Consider a population of individuals whose

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

has only two genes, ''a'' and ''b''. If an advantageous mutant (''A'') of gene ''a'' arises in a given individual, that individual's genes will through natural selection become more frequent in the population over time. However, if a separate advantageous mutant (''B'') of gene ''b'' arises before ''A'' has gone to fixation, and happens to arise in an individual who does not carry ''A'', then individuals carrying ''B'' and individuals carrying ''A'' will be in competition. If recombination is present, then individuals carrying both A and B (of genotype AB) will eventually arise. Provided there are no negative

epistatic Epistasis is a phenomenon in genetics in which the effect of a gene mutation is dependent on the presence or absence of mutations in one or more other genes, respectively termed modifier genes. In other words, the effect of the mutation is depe ...

effects of carrying both, individuals of genotype ''AB'' will have a greater selective advantage than ''aB'' or ''Ab'' individuals, and ''AB'' will hence go to fixation. However, if there is no recombination, AB individuals can only occur if the latter mutation (B) happens to occur in an Ab individual. The chance of this happening depends on the frequency of new mutations, and on the size of the population, but is in general unlikely unless A is already fixed, or nearly fixed. Hence one should expect the time between the A mutation arising and the population becoming fixed for AB to be much longer in the absence of recombination. Hence recombination allows evolution to progress faster. ote: This effect is often erroneously equated with "clonal interference", which happens when ''A'' and ''B'' mutations arise in different wild type (''ab'') individuals and describes the ensuing competition between ''Ab'' and ''aB'' lineages.] There tends to be a correlation between the rate of recombination and the likelihood of the preferred haplotype (in the above example labeled as ''AB'') goes into fixation in a population.

Joe Felsenstein Joseph "Joe" Felsenstein (born May 9, 1942) is a Professor Emeritus in the Departments of Genome Sciences and Biology at the University of Washington in Seattle. He is best known for his work on phylogenetic inference, and is the author of ''Infer ...

(1974) showed this effect to be mathematically identical to the Fisher–Muller model proposed by R. A. Fisher (1930) and H. J. Muller (1932), although the verbal arguments were substantially different. Although the Hill-Robertson effect is usually thought of as describing a disproportionate buildup of fitness-reducing (relative to fitness increasing) LD over time, these effects also have immediate consequences for mean population fitness.

References

{{DEFAULTSORT:Hill-Robertson Effect Genetics in the United Kingdom Population genetics Evolutionary biology

Explanation

See also

References