Appendix E: Basics of Molecular Phylogeny

CS Mukhopadhyay and RK Choudhary

School of Animal Biotechnology, GADVASU, Ludhiana

Phylogenetic analysis indicates the splits and diversions of species within ancestral lines, leading to a procreation of a clade. The term “clade” means a cluster of two or more species related by a common ancestor. The principle of phylogeny is relatedness among various organisms, due to descending from a nearer or remote common ancestor (CA). Thus, phylogeny is the relationship among different organisms due to sharing of a recent common ancestor (Zimmermann, 1931). It is a method by which to obtain an idea of the evolution and origin of an organism. The term “phylogeny” originates from two Greek words: Phylon (Stem) and Genesis (Origin).


This is based on the regularity of the decay process of radioactive elements. Suppose an ancient rock which has been lying undisturbed is tested, using a mass spectrophotometer, for the amount of radioactive uranium (235U) and normal lead (207Pb). The former is decayed into the latter, with a half‐life of 710 million years (MY) (Guttman, 2007). The wider the ratio of uranium to lead, the older the rock is. Thus, the approximate time of fossilization of an individual can be estimated by geological study, and this forms the geological clock. It is thought‐provoking to note that the first fossil evidence for many of the animal phyla is available from the rocks preserved since the Cambrian Period of ...

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