| Fifteen genes of the hierarchy that control limb development were examined by natural selection analyses, rate analysis, codon bias, GC content, and nucleotide diversity tests to evaluate the hypotheses that the genes show neutral substitutions, are not undergoing codon bias or GC richness, show no change in diversity between the fishes and the tetrapods, and have equivalent evolutionary rates. The genes did not show neutral substitutions except for hox-c6 and formin, were not undergoing codon bias or GC richness, had a difference in the nucleotide diversities between the fish and tetrapods, and the evolutionary rates of the genes differed. The genes found to be involved in the transition from fins to limbs were shh, fgf-4, myf-5, myoD, and tnt. Results indicate the limb form is genetically conserved until after the creation and initiation of the apical ectodermal ridge and the zone of polarizing activity. |
