figure 1: The limbs of vertebrates is an example of homolgy
Homology is the sharing of structures, genes, or proteins, between different species. [1] There are two branches of homologues, orthologues and paralogues. Orthologues are found in separate species through speciation events, whereas paralogues are homologous genes resulting from a gene duplication within a specie.[2] An example illustration of the principle of homology is the bone structure between different vertebrates shown in Fig.1. Even though their functions may change, they still share a common ancestor. Homologues can be scored using percent identity scores, which is the percent of a particular sequence from human that matches with sequence from another species.