Molecular evidence is now central to classification. Because DNA is inherited, species that shared a common ancestor recently have had less time for mutations to build up, so their molecules are more similar.DNA analysis
The base sequences of the same gene, or of whole genomes, are compared between species. The more similar the base sequences, the more closely the species are related. DNA gives the most detailed evidence, because it also includes changes that do not alter proteins: the genetic code is degenerate, so some base changes do not change the amino acid coded for.Proteomics
The proteome is the full set of proteins made by a cell or organism. Proteomics is the study of the proteome, including the amino acid sequences of proteins. The base sequence of a gene codes for the amino acid sequence of a protein, so differences in amino acid sequence arise from differences in the DNA base sequence. Comparing the amino acid sequences of the same protein in different species shows how closely they are related: fewer differences mean a more recent common ancestor.Worked example: cytochrome c, a respiratory protein found in almost all eukaryotes, is often compared. Human cytochrome c is identical to chimpanzee cytochrome c, differs from rhesus monkey cytochrome c by 1 amino acid and from horse cytochrome c by 12. So humans are most closely related to chimpanzees, then rhesus monkeys, then horses.Molecular evidence is objective and quantitative, and it has led to many groups being reclassified.
The base sequences of the same gene, or of whole genomes, are compared between species. The more similar the base sequences, the more closely the species are related. DNA gives the most detailed evidence, because it also includes changes that do not alter proteins: the genetic code is degenerate, so some base changes do not change the amino acid coded for.Proteomics
The proteome is the full set of proteins made by a cell or organism. Proteomics is the study of the proteome, including the amino acid sequences of proteins. The base sequence of a gene codes for the amino acid sequence of a protein, so differences in amino acid sequence arise from differences in the DNA base sequence. Comparing the amino acid sequences of the same protein in different species shows how closely they are related: fewer differences mean a more recent common ancestor.Worked example: cytochrome c, a respiratory protein found in almost all eukaryotes, is often compared. Human cytochrome c is identical to chimpanzee cytochrome c, differs from rhesus monkey cytochrome c by 1 amino acid and from horse cytochrome c by 12. So humans are most closely related to chimpanzees, then rhesus monkeys, then horses.Molecular evidence is objective and quantitative, and it has led to many groups being reclassified.