Ancient origin of lactalbumin from lysozyme: Analysis of DNA and amino acid sequences

Summary Parsimony trees relating DNA sequences coding for lysozymesc and -lactalbumins suggest that the gene duplication that allowed lactalbumin to evolve from lysozyme preceded the divergence of mammals and birds. Comparisons of the amino acid sequences of additional lysozymes and lactalbumins are consistent with this view. When all base positions are considered, the probability that the duplication leading to the lactalbumin gene occurred after the start to mammalian evolution is estimated to be 0.05–0.10. Elimination of the phylogenetic noise generated by fast evolution and compositional bias at third positions of codons reduced this probability to 0.002–0.03. Thus the gene duplication may have long preceded the acquisition of lactalbumin function.