Question

Relationship among different organism can be shown by molecular phylogeny match of its classification scheme. Explain

Answer 1

Recount how taxonomy led to phylogeny and discuss the reasons why molecular markers are important in phylogenetics

Describe the key features of a phylogenetic tree and distinguish between inferred trees, true trees, gene trees and species trees

Explain how phylogenetic trees are reconstructed, including a description of DNA sequence alignment, the methods used to convert alignment data into a phylogenetic tree, and how the accuracy of a tree is assessed

Discuss, with examples, the applications and limitations of molecular clocks

Give examples of the use of phylogenetic trees in studies of human evolution and the evolution of the human and simian immunodeficiency viruses

Describe how molecular phylogenetics is being used to study the origins of modern humans, and the migrations of modern humans into Europe and the New World

if genomes evolve by the gradual accumulation of mutations, then the amount of difference in nucleotide sequence between a pair of genomes should indicate how recently those two genomes shared a common ancestor. Two genomes that diverged in the recent past would be expected to have fewer differences than a pair of genomes whose common ancestor is more ancient. This means that by comparing three or more genomes it should be possible to work out the evolutionary relationships between them. These are the objectives of molecular phylogenetics.

16.1. The Origins of Molecular Phylogenetics

Molecular phylogenetics predates DNA sequencing by several decades. It is derived from the traditional method for classifying organisms according to their similarities and differences, as first practiced in a comprehensive fashion by Linnaeus in the 18th century. Linnaeus was a systematicist not an evolutionist, his objective being to place all known organisms into a logical classification which he believed would reveal the great plan used by the Creator - the Systema Naturae. However, he unwittingly laid the framework for later evolutionary schemes by dividing organisms into a hierarchic series of taxonomic categories, starting with kingdom and progressing down through phylum, class, order, family and genus to species. The naturalists of the 18th and early 19th centuries likened this hierarchy to a ‘tree of life’ (Figure 16.1), an analogy that was adopted by Darwin (1859) in The Origin of Species as a means of describing the interconnected evolutionary histories of living organisms. The classificatory scheme devised by Linnaeus therefore became reinterpreted as a phylogeny indicating not just the similarities between species but also their evolutionary relationships.