Being of the same typical structure; having like relations to a fundamental type to structure; as, those bones in the hand of man and the fore foot of a horse are homologous that correspond in their structural relations, that is, in their relations to the type structure of the fore limb in vertebrates.
Nucleic acid molecules with the same base sequence except for minor differences in alleles; (ii) nucleic acid molecules originating from strains of the same species, thus having at least long stretches of identical DNA base sequences; (iii) gene or protein families having a recognizable common evolutionary origin.
In phylogenetics, describing particular features in different individuals that are genetically descended from the same feature in a common ancestor. In molecular biology, often "homologous" simply means similar, regardless of genetic relationship.
Shared by virtue of inheritance from a common ancestor. A character or character state shared by two organisms (which may represent different species or clades) is said to be homologous if that character or character state was present in all of their ancestors back to and including their most recent common ancestor.
Describing the relationship between a pair of structures or processes that show a fundamental similarity because of their having descended from a common ancestor. Homologous structures in related species have the same evolutionary origin although their functions may differ widely: e.g. the flipper of a seal and the wing of a bat. Homologous genes in a genome share a similar DNA base sequence because they arose by duplication of an ancestral gene.
Descended from a common ancestor. Defined in 1843 by Richard Owen, the British Palaeontologist as the "same organ under every variety of form and function". For molecular sequence data, it is taken to mean that two sequences or even two characters within sequences are descended from a common ancestor. This term is frequently mis-used as a synonym for 'similar', as in "two sequences were 70% homologous". This is totally incorrect! Sequences show a certain amount of similarity. From this similarity value, we can probably infer that the sequences are homologous or not. A statement that is attributed to Walter Fitch is that (I'm prarphrasing here) homology is like pregnancy. You are either pregnant or not, two sequences are either homologous or they are not.
In phylogenetics, describing particular features in different individuals that are genetically descended from the same feature in a common ancestor. In molecular biology, homologous sequences often mean significantly similar sequences that are highly likely to have a common descent.
A pair of genes, traits, or structures from different, but related, species from a common ancestral organism which are identical or very similar to each other. The shared commonality may not necessarily perform the same functions in each organism, nor perform the functions it did in the common ancestor. Back to glossary index
description for physical features that are formed in similar ways during embryonic development and that have a similar structure (e.g., the flipper of a whale, the arm of a human and the wing of a bat are all homologous organs)
similarity in the sequence of a protein or nucleic acid or in the structure of an organ that reflects a common evolutionary origin. Molecules or sequences that exhibit homology are referred to as homologs. In contrast, analogy is a similarity in structure or function that does not reflect a common evolutionary origin. (Molecular Cell Biology/Harvey Lodish [et al.] - 4th)
In chromosomes, a pair of chromosomes that contain the same gene (although perhaps different alleles). There are 23 pairs of homologous chromosomes in humans; one of each was contributed by each parent.