Intragenomic conflict

The selfish gene theory postulates that natural selection will increase the frequency of those genes whose phenotypic effects ensure their successful replication. Generally, a gene achieves this goal by building, in cooperation with other genes, an organism capable of transmitting the gene to descendants. Intragenomic conflict arises when genes inside a genome are not transmitted by the same rules, or when a gene causes its own transmission to the detriment of the rest of the genome (this last kind of gene is usually called a selfish genetic element, ultraselfish gene, or parasitic DNA).

These "gene-centric" mechanisms of natural selection explain a few features of genetics which are not explained by the traditional "organism-centric" view, which only takes into account the effect of the phenotype on the reproductive success of the organism as a whole.

This section deals with conflict between nuclear genes.

In principle, the two parental alleles have equal probabilities of being present in the mature gamete. However, there are several mechanisms that lead to an unequal transmission of parental alleles from parents to offspring. One example is a gene, called a segregation distorter, that "cheats" during meiosis or gametogenesis and thus is present in more than half of the functional gametes. The most studied examples are sd in Drosophila melanogaster (fruit fly),t haplotype in Mus musculus (mouse) and sk in Neurospora spp. (fungus). Possible examples have also been reported in humans. Segregation distorters that are present in sexual chromosomes (as is the case with the X chromosome in several Drosophila species) are denominated sex-ratio distorters, as they induce a sex-ratio bias in the offspring of the carrier individual.

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