HOMOLOGY

homology

(noun) the quality of being similar or corresponding in position or value or structure or function

Source: WordNet® 3.1

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Etymology

Noun

homology (countable and uncountable, plural homologies)

A homologous relationship.

(topology) A theory associating a system of groups to each topological space.

(algebra) A certain system of groups associated to a chain complex.

(chemistry) The relationship between the elements in the same group of the periodic table, or between organic compounds in a homologous series.

(evolutionary theory) A correspondence of structures in two life forms with a common evolutionary origin, such as flippers and hands.

(genetics) The presence of the same series of bases in related genes.

Usage notes

• (evolutionary theory)

For a discussion of the use of the term homology (and homologous) in biology, see: Patterson, Colin. "Homology in Classical and Molecular Biology." Molecular Biology and Evolution 5, no. 6 (November 1988): 603–625.

• (topology)

When used attributively with the name of a topological space (such as in the terms homology n-sphere and homology manifold) the reference is to a space whose homology is the same as that of the named space: thus, for example, a homology manifold is a space whose homology is that of some manifold.

Sometimes used to mean homology group: thus, X did Y by computing the homology of Z means X did Y by computing the homology groups of Z.

More loosely, the term homology in a space refers to a singular homology group (group of singular homologies).

Source: Wiktionary

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Ho*mol"o*gy, n. Etym: [Gr. Homologous.]

1. The quality of being homologous; correspondence; relation; as, the homologyof similar polygons.

2. (Biol.)

Definition: Correspondence or relation in type of structure in contradistinction to similarity of function; as, the relation in structure between the leg and arm of a man; or that between the arm of a man, the fore leg of a horse, the wing of a bird, and the fin of a fish, all these organs being modifications of one type of structure.

Note: Homology indicates genetic relationship, and according to Haeckel special homology should be defined in terms of identity of embryonic origin. See Homotypy, and Homogeny.

3. (Chem.)

Definition: The correspondence or resemblance of substances belonging to the same type or series; a similarity of composition varying by a small, regular difference, and usually attended by a regular variation in physical properties; as, there is an homology between methane, CH4, ethane, C2H6, propane, C3H8, etc., all members of the paraffin series. In an extended sense, the term is applied to the relation between chemical elements of the same group; as, chlorine, bromine, and iodine are said to be in homology with each other. Cf. Heterology. General homology (Biol.), the higher relation which a series of parts, or a single part, bears to the fundamental or general type on which the group is constituted. Owen.

– Serial homology (Biol.), representative or repetitive relation in the segments of the same organism, -- as in the lobster, where the parts follow each other in a straight line or series. Owen. See Homotypy.

– Special homology (Biol.), the correspondence of a part or organ with those of a different animal, as determined by relative position and connection. Owen.

Source: Webster’s Unabridged Dictionary 1913 Edition

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