2R Hypothesis - Ohno's Argument

Ohno's Argument

Ohno presented the first version of the 2R hypothesis as part of his larger argument for the general importance of gene duplication in evolution. 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". He later added to this argument the evidence that most paralogous genes in vertebrates do not demonstrate genetic linkage. Ohno argued that linkage should be expected in the case of individual tandem duplications (in which a duplicate gene is added adjacent to the original gene on the same chromosome), but not in the case of chromosome duplications.