ABSTRACT
The study of molecular evolution was made possible when entire sequences of some important proteins – like cytochrome C, insulin and the globins – became available and homologous proteins in different organisms could be compared. Due to the direct relationship between the amino-acid sequence and the DNA coding for it, through the genetic code, it was possible to reconstruct the DNA sequences. One of the first molecular studies of protein evolution was the comprehensive study of Cytochrome C. The rate of molecular evolution was first calculated from the number of amino-acid replacement in proteins. It is calculated from comparisons of DNA sequences of homologous genes in different organisms, which are stored in data banks. The calculation of evolutionary rate is based on the fundamental assumption that the compared genes diverged from a common ancestor, and that the observed sequence differences between them are due to accumulated mutations.
