Homology refers to the similarity between two nucleic acid molecules nucleotide The degree of similarity between sequences or between amino acid sequences of two protein molecules. Sequence analysis is the final method to determine the degree of homology, and DNA DNA hybridization or DNA RNA hybridization is also a useful estimation approach. [1] Homology is a central concept in comparative biology. The most basic meaning of homology is to have a common ancestor. Generally speaking, if two traits (states) of two species meet any of the following two conditions, they can be called a pair of homologous traits:
(1) They are identical to a certain personality found in the ancestral group of these species;
(2) They are different characters with ancestor descendant relationship. [1]
Intrinsic due to common evolutionary or ontogenetic sources Similarity , but their functions are not necessarily the same, such as the forelimbs of dogs and the wings of birds. At the molecular level, it refers to two nucleic acid molecules nucleotide Sequence or two protein molecules amino acid The degree of similarity between sequences. Although homology must be Sequencing But DNA - DNA or DNA - RNA hybridization can provide valuable estimates. 
