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, 23:06, 8 September 2010
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| Across the entire genome the ratio of transitions to transversions is typically around 2. In protein coding regions, this ratio is typically higher, often a little above 3. The higher ratio occurs because, especially when they occur in the third base of a codon, transitions are much more likely to change the encoded amino acid. A refinement to this analysis, in protein coding regions, is to examine the transition to transversion ratio separately for non-degenerate, two-fold degenerate, three-fold degenerate and four-fold degenerate sites. | | Across the entire genome the ratio of transitions to transversions is typically around 2. In protein coding regions, this ratio is typically higher, often a little above 3. The higher ratio occurs because, especially when they occur in the third base of a codon, transitions are much more likely to change the encoded amino acid. A refinement to this analysis, in protein coding regions, is to examine the transition to transversion ratio separately for non-degenerate, two-fold degenerate, three-fold degenerate and four-fold degenerate sites. |
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− | === Why Are Reciprocal Changes Not Equally Frequent? ===
| + | == Why Are Reciprocal Changes Not Equally Frequent? == |
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| One of the most surprising features of many variant lists in humans is that C->T changes (C reference, T variant) are more frequent than T->C changes. Likewise, G->A changes are more frequent than A->G changes. | | One of the most surprising features of many variant lists in humans is that C->T changes (C reference, T variant) are more frequent than T->C changes. Likewise, G->A changes are more frequent than A->G changes. |