Evolution: The Case of the Glyceraldehyde-3-Phosphate Dehydrogenase Gene
  The enzyme Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) catalyses the decomposition of glucose. The gene that produces the GAPDH is therefore present in a wide class of organisms. We show that for this gene the average value of the fluctuations in nucleotide distribution in the codons, normalized to strand bias, provides a reasonable measure of how the gene has evolved in time. 
Sujay Chattopadhyay, Satyabrata Sahoo and Jayprokas Chakrabarti