Genetic equidistance at the nucleotide level

Abstract

The genetic equidistance phenomenon was first discovered in 1963 by Margoliash and shows complex taxa to be all approximately equidistant to a less complex species in amino acid percentage identity. The result has been mis-interpretated by the ad hoc universal molecular clock hypothesis, and the much overlooked mystery was finally solved by the maximum genetic diversity hypothesis (MGD). Here, we studied 15 proteomes and their coding DNA sequences (CDS) to see if the equidistance phenomenon also holds at the CDS level. We performed DNA alignments for a total of 5 groups with 3 proteomes per group and found that in all cases the outgroup taxon was equidistant to the two more complex taxa species at the DNA level. Also, when two sister taxa (snake and bird) were compared to human as the outgroup, the more complex taxon bird was closer to human, confirming species complexity rather than time to be the primary determinant of MGD. Finally, we found the fraction of overlap sites where coincident substitutions occur to be inversely correlated with CDS conservation, indicating saturation to be more common in less conserved DNAs. These results establish the genetic equidistance phenomenon to be universal at the DNA level and provide additional evidence for the MGD theory.