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Next, 2R ohnologs in the human genome are prone to dominant deleterious mutations and frequently implicated in cancer and genetic diseases. The genes that remain typically belong to vast gene-complexes scattered across the genome, usually no more than a handful.

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Data from additional gene families revealed a common one-to-many rule when amphioxus and vertebrate genes were compared. It is also referred to as an event more often than a hypothesis. Based on relative genome sizes and isozyme analysis, he suggested that ancestral fish or amphibians had undergone at least one and possibly more cases of "tetraploid evolution".

It is not disputed that human chromosomes bear sets of genes related to sets of genes on other chromosomes ; the controversy centres on whether they were generated by large-scale duplications that doubled all the genes at the same time, or whether a series of individual gene duplications occurred followed by 2r hypothesis rearrangement to shuffle sets of genes together.

Next, there is a consensus that whole-genome duplications are generally followed by periods of rapid gene loss.

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When considering only this subset of 3,plus early vertebrate duplications, they found a global pattern of human genome segments with similar arrangements of paralogous genes and multiple chromosomes with long linear stretches of interdigitated sets of paralogous genes—evidence that the duplications occurred in large segments.

Second, cloning of Hox genes in amphioxus revealed presence of a single Hox gene cluster[10] in contrast to the four clusters in humans and mice. A third event in vertebrates, known as 3R, occurred in stem-teleosts. Pattern predicted for the relative locations of paralogous genes from two genome duplications [11] Controversy about the 2R hypothesis hinged on the nature of paralogy regions.

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But did these early duplication events arise from some large-scale duplication event, or were they simply the result of a great number of smaller scale duplications? Variations in the number and timings of genome duplications typically still are referred to as examples of the 2R hypothesis.

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There is a large body of research on this. He later added to this argument the evidence that most paralogous genes in vertebrates do not demonstrate genetic linkage.

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In the lede it says, "Variations in the number and timings of genome duplications typically still are referred to as examples of the 2R hypothesis.

The observation that some gene families have four members in vertebrates but just one in invertebrates the 4: As for the timing, everyone agrees that hagfish and lampreys inherited ohnologs from 2R and that lancelets and tunicates did not.

The name "2R hypothesis" is becoming obsolete.

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Open in a 2r hypothesis window The evolutionary patterns of gene duplications were reconstructed by comparing the complete gene sets of a tunicate sea squirtfish, mouse, and human. Published online Sep 6.

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Whole genome duplications are a basic fact of evolutionary biology. And because duplicate genes are far more likely to degrade than to assume new or shared functions, the signal of whole genome duplication disappears.

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Even stronger support for the 2R hypothesis comes from the observation that the colinear arrangement of these genes is predominantly in a 4-fold pattern; this repetitive pattern is seen across almost all the human chromosomes. Ohno also proposed that two rounds of whole genome duplication occurred at some point in early vertebrate evolution—a possibility that could explain the relatively large size and complexity of the vertebrate genome.

It's unlikely, the authors argue, that any combination of smaller, independent duplication events could have generated the same pattern.

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