HOMOLOGY (Greek ομολογ? Α - correspondence) in biology, the correspondence of organs and structures in organisms, due to a common origin. The initial similarity of the structure of homologous formations can be veiled for the second time by differences that have arisen in the course of evolution in connection with the development of different adaptations and the acquisition of new functions. For example, the auditory ossicles in the middle ear of mammals (stapes, incus, and malleus) are homologous, respectively, to the hyomandibular, square, and articular bones of the visceral skull of other vertebrates. Homology as a primary similarity based on kinship is opposed to analogy - a secondary similarity that arises in different (including not related to each other) species during the development of similar adaptations. He gave a definition of homology and contrasted its analogy with R. Owen (1843). The evolutionary meaning of homology phenomena was explained by Charles Darwin (1859). The proof of the homology of organs in different species is based on 4 most important criteria: the similarity of the morphological plan of the structure of organs; the similarity of their position in the body in relation to other organs; the similarity of their development in ontogeny; evolutionary succession of intermediate forms up to a common ancestral state. German zoologist and anatomist K. Gegenbaur (1898) called the homology of organs in different species "partial homology", opposing it to "general homology", which means the correspondence of structures in one organism arising from similar embryonic primordia and occupying a similar position in relation to the axis or a plane of symmetry. There are 3 forms of general homology: homodynamy, homotypy and homonomy.

In the 20th century, the term "homology" was also used to denote the correspondence of genes and processes of morphogenesis leading to the formation of homologous organs. However, in distantly related species of organisms, there is no simple correspondence between gene homology and organ homology, since the development of complex structures of the organism is controlled by many genes interacting in ontogenetic processes, and changes in some genes can be compensated for by the influence of others. Therefore, gene homology and organ homology are independent categories. A special category is also represented by chromosome homology - the correspondence of chromosomes carrying the same sets of homologous genes (although homologous genes can be represented by different alleles).

Lit .: Gilyarov M.S. Modern concepts of homology // Successes of modern biology. 1964. T. 57. No. 2; Blyakher L. Ya. Problems of animal morphology. M., 1976; Iordansky N.N. Homology and analogy // Biology at school. 1991. No. 5.

from the Greek. ???????? - agreement, compliance) - the similarity of the most important properties that reveal the essence of the corresponding objects. This essence can be the same, despite the apparent external differences. G. can be contrasted with analogy as similarity in one or a number of properties that are not necessarily essential for the things being compared. The term "G." used in a similar sense in a number of sciences. In biology, G. is understood as a similarity in the structure and origin of organs, which can nevertheless have a different appearance and carry different functions (for example, the wing of a bird is homologous to the forepaw of a mammal, while the wing of a bird and the wing of a butterfly are only similar organs with a similar function, but different structure and origin). The idea of ​​homologous organs contributed to the development of evolutionary views in biology, the establishment of genetic. connections of organisms. C. Darwin noted that homologous organs tend to change in the same direction, which confirms their relationship. This circumstance allowed N. Vavilov to make a number of successful predictions about the existence of plants with previously unknown traits, which is emphasized by practical. the meaning of G. The meaning of the concept "G." is great. for chem. sciences. In inorganic In chemistry, homologous are the series of similar elements (eg, lithium, sodium, potassium, rubidium) or ions (eg, ClO4, MnO4, BF4). Especially often the concept of "G." applies to the ranks of chem. compounds, constructed in such a way that the members of the series differ from each other by a certain structural unit, taken n times. For the simplest case, the usual homologous. rows of organic In chemistry, such a unit is the methylene group (CH2). However, this group can be more complex, what leads? the emergence of other series of higher homologues (for example, vinylogs, phenylogs, carbinologists). Homologous. series are important for understanding the laws of chemistry. connections. Taking into account the similarity of homologues, one can determine the properties of a number of substances, including unknown ones, from one compound. However, between the members of the homologous. A number of differences also take place, caused, as F. Engels noted, by the transition of quantitative changes to qualitative changes with an increase or decrease in the number of structural units of the same type. G. shows specific. the form of action of the indicated law of dialectics, when, during quantitative-qualitative transitions, a certain general qualitative regularity of a number of chemical compounds is preserved. compounds that have the same function. In homologous rows represent a special type of discreteness of matter. If inside the atom, the units of discrete changes are nuclear particles (protons and neutrons), if in inorganic. chemistry such discrete units are atoms, then homologous. ranks of organic compounds represent a higher type of complication of a substance, when a unit of discreteness, a measure of the transition from one compound to another, becomes first a simple methylene, and then more and more complex groups and radicals. Yu. Zhdanov. Rostov-on-Don. A. Uemov. Ivanovo. ...

Used in cases where two similar organs or genes do not have a common predecessor is analogy.

Homology in Comparative Anatomy

History of the concept

"... a part or organ in one animal that has the same function as another part or organ in a different animal ..."
[a part or organ of an animal that has the same function as another part or organ in another animal]

and homologous structures:

"The same organ in different animals under every variety of form and function ..."
[the same organ in different animals with all variations in form and function]

Examples of similar structures include the wings of insects and birds. Examples of homologous ones are a bird's wing and a human hand. With the concept of homology, Owen associated the concept of an archetype or building plan. By comparing skeletons, Owen reconstructed the archetype of the vertebrate and the archetypes of each of the then recognized classes of vertebrates (fish, reptiles, birds and mammals). He considered skeletons of specific vertebrates as real incarnations of these archetypes. Following his example, Thomas Huxley reconstructed the archetype (building plan) of molluscs. The search for building plans for different groups of animals and plants became one of the most important tasks of comparative anatomy in the second half of the 19th century.

It should be noted that even before Owen's work, attempts were made to formalize the procedure for comparing living beings and to develop general principles of comparative anatomy. Thus, Etienne Geoffroy Saint-Hilaire in his work Anatomical philosophy developed analog theory and formulated connectivity law... Starting from the teachings of Aristotle about analogies, he tried to give the concept analogue greater rigor, to find criteria and parameters of comparison, suggesting to name the organs that occupy a similar position relative to other organs in the compared organisms. On the basis of this theory, he was, in fact, one of the first to begin establishing homology. In his constructions, E. Geoffroy Saint-Hilaire was often carried away (for example, he argued that the organization of arthropods and vertebrates is based on a general structure plan, only in arthropods the insides are inside, and not outside of the spine). His students also developed ideas about the unity of the structural plan of all animals, including mollusks and vertebrates, which served as one of the reasons for the famous discussion between E. Geoffroy Saint-Hilaire and Georges Cuvier (1830).

• Position criterion. Homologous parts are those that occupy a similar position relative to other parts of the body. For example, with all the differences in the shape of the skulls of a whale and a person, the bones that make up them are located relative to each other in a similar way.
• Special quality criterion. Only those structures that are similar in their thin structure can be considered homologous (for example, adipose tissue arising at the site of the removed eye is not homologous to the eye, although it takes its place, corresponding to the first criterion).
• Criterion for transitional forms. If two forms are not similar to each other, but are connected by a continuous series of "transitional forms", then they can be considered homologous.

Other homology criteria

• Composition criterion... Homologous organs are considered to be organs consisting of similar and similarly spaced parts relative to each other (for example, the location of bones in the limbs of vertebrates). This criterion essentially coincides with the second criterion of Remane.
• Development criterion... Organs that develop in a similar way from the same embryonic primordia are considered homologous.
• Genetic criterion... Homologous structures are considered to be structures based on the development of the same genetic program (a system of interacting genes) inherited from common ancestors.

Related and derived concepts

Oligomerization of homologous (homodynamic) organs

Oligomerization of homologous (homodynamic) organs - Dogel's principle- the process (in the course of animal evolution) of reducing the number of homologous and homodynamic formations to a certain definite number, associated with the intensification of the functions of the system. It is realized in the evolution of all the main phylogenetic trunks of multicellular animals, accompanied by their progressive morphological and functional differentiation.

The principle of multiple laying of newly formed organs Dogel - new organs arise (for example, due to a change in lifestyle - the transition from a sedentary lifestyle to a mobile one or from aquatic to terrestrial), usually in a large number, poorly developed, homogeneous and often arranged without a certain order. As they differentiate, they acquire a certain localization, quantitatively decreasing to a constant number for a given taxonomy. For example, segmentation of the body in the type of annelids is multiple and unsteady. All segments are homogeneous. In arthropods (descended from annelids), the number of segments in most classes decreases, becomes constant, individual body segments, usually combined into groups (head, chest, abdomen, etc.), specialize in performing certain functions.

Finding out whether they retain a multiple character or have already undergone oligomerization of certain organs allows us to judge the degree of antiquity of their origin. By the combination of organs of different ages, one can sometimes judge the phylogeny.

Homology in Comparative Genomics

Homologous DNA Sequences

Simplified diagram of the evolution of globins.

Each rectangle corresponds to a globin gene. The nodes of the evolutionary tree are marked with Roman numerals.
All globins originate from a single precursor and, therefore, are homologues - orthologues of protoglobin. Hemoglobins are paralogs of myoglobins, since they originated from the protoglobin gene after its duplication (on the evolutionary segment between nodes I and II). For example, human hemoglobins are paralogs in relation to each other: they all arose as a result of duplications and the subsequent accumulation of mutations. Human hemoglobins α1 and α2 are orthologues of shark and chicken α hemoglobins, as they come from the pro-α-hemoglobin of a common ancestor located in node II. The same is true for β-hemoglobins. In this case, human α-hemoglobins can be called paralogs, in relation to not only human, but also shark and chicken β-hemoglobins, since both of these series of orthologues ultimately go back to the same protohemoglobin that arose in the segment I-II.

Comparative analysis of the sequences of nucleotides in DNA and amino acids in proteins required the development of the traditional concept of homology. When analyzing sequences, it is customary to distinguish orthology and paralogy(and correspondingly, orthologs and paralogs).

Homologous sequences are called orthologous, if the act of speciation led to their separation: if a gene exists in a species that diverges to form two species, then copies of this gene in daughter species are called orthologs... Homologous sequences are called paralogous, if a gene duplication led to their separation: if a gene duplication occurred as a result of a chromosomal mutation within one organism, then its copies are called paralogs.

Orthologs usually have identical or similar functions. This is not always the case with paralogs. Due to the lack of selection pressure on one of the copies of the duplicated gene, this copy is able to mutate further without hindrance, which can lead to the emergence of new functions.

For example, the genes encoding myoglobin and hemoglobin are usually considered ancient paralogs. Likewise, the known hemoglobin genes (α, β, γ, etc.) are paralogs of each other. While each of these genes serves the same basic oxygen transport function, their functions have already diverged somewhat: fetal hemoglobin (fetal hemoglobin with the α 2 γ 2 subunit structure) has a greater affinity for oxygen than adult hemoglobin (α 2 β 2). Protein alignment, the essence of which is to find, using various algorithms, the most conserved residues in these sequences, which are usually key for the performance of one or several functions of a protein, to study the domain structure of a given protein by searching for known structural motifs and domains in the protein under study. ... Also, using various databases, one can search for a homologue of a given protein in various organisms, build a phylogenetic tree of various protein sequences, and the like.

It should be noted that the sometimes used terms "percent homology" and "significant homology" are erroneous, since sequence homology is a qualitative concept, but not quantitative. Homologous proteins, for example, can retain only 10% of identical amino acids, while non-homologous proteins have 30% of them.

Homologous chromosomes

Homologous chromosomes in a diploid cell are paired chromosomes, each of which is inherited from one of the parents. With the exception of the sex chromosomes in the heterogametic sex, the nucleotide sequences in each of the homologous chromosomes have significant similarity along their entire length. This means that they typically contain the same genes in the same sequence. Sex chromosomes in the heterogametic sex also have homologous regions (although they occupy only part of the chromosome). In terms of sequence analysis, sex chromosomes should be counted. The description of the patterns of hereditary variations made it possible to predict and purposefully search for homologous mutations that have not yet been identified in different species of cultivated plants, which led to the intensification of Notes

Literature

• Beklemishev V.N. Taxonomy methodology. M., 1994.
• Blyakher L. Ya.Analogy and homology, in the collection: Development idea in biology. M., 1965.
• Darwin Ch. The origin of species by natural selection, Soch., Vol. 3. M.-L., 1939.
• Mamkaev Yu.V. Homology and analogy as fundamental concepts of morphology
• Shmalgauzen I. I. Fundamentals of Comparative Anatomy of Vertebrates. 2nd ed. M., 1935.
• Haeckel, E. Generelle Morphologie der Organismen. Bd 1-2. Berlin, 1866.
• Gegenbaur, G. Vergleichende Anatomie der Wirbelthiere ... Leipzig, 1898.
• Owen, R. On the archetype and homologies of the vertebrate skeleton. London, 1847.

Relevant facilities. This essence can be the same, despite the apparent external differences. G. can be contrasted with analogy as similarity in one or a number of properties that are not necessarily essential for the things being compared. The term "G." used in a similar sense in a number of sciences. In biology, G. is understood as a similarity in the structure and origin of organs, which can nevertheless have different external and carry different functions (for example, the wing of a bird is homologous to the forepaw of a mammal, while the wing of a bird and the wing of a butterfly are only analogous organs , having a similar function, but different structure and origin). The idea of ​​homologous organs contributed to the development of evolutionary views in biology, the establishment of genetic. connections of organisms. C. Darwin noted that homologous organs tend to change in the same direction, which confirms their relationship. This circumstance allowed N. Vavilov to make successful predictions about the existence of plants with previously unknown traits, which is emphasized by practical. G.

The meaning of the concept "G." is great. for chem. sciences. In inorganic In chemistry, homologous are the series of similar elements (eg, lithium, sodium, potassium, rubidium) or ions (eg, ClO4, MnO4, BF4).

Especially often "G." applies to the ranks of chem. compounds, constructed in such a way that the members of the series differ from each other by a certain structural unit, taken n times. For the simplest case, the usual homologous. rows of organic chemistry, such a unit is methylene (CH2). However, this group may be more complex, which leads to the emergence of other series of higher homologues (for example, vinylogs, phenylogs, carbinologists).

Homologous. series are important for understanding the laws of chemistry. connections. Taking into account the similarity of homologues, it is possible to identify a number of substances, including unknown ones, by one compound. However, between the members of the homologous. A number of differences also have differences, caused, as F. Engels noted, by the transition of quantitative changes to qualitative changes with an increase or decrease in the number of structural units of the same type. G. shows specific. the form of action of this law, when, during quantitative and qualitative transitions, a certain general qualitative regularity of a number of chemical compounds is preserved. compounds that have the same function.

In homologous the series represents a special discreteness of matter. If inside the atom, the units of discrete changes are nuclear particles (protons and neutrons), if in inorganic. chemistry such discrete units are atoms, then homologous. ranks of organic compounds represent a higher type of complication of a substance, when a unit of discreteness, a measure of the transition from one compound to another, becomes first a simple methylene, and then more and more complex groups and radicals.

Yu. Zhdanov. Rostov-on-Don.

A. Uemov. Ivanovo.

Philosophical Encyclopedia. In 5 volumes - M .: Soviet encyclopedia. Edited by F.V. Konstantinov. 1960-1970 .

See what "HOMOLOGY" is in other dictionaries:

Homology ... Spelling dictionary-reference

- (Greek). The similarity based on the same elements of the structure of organisms, in contrast to the analogy resulting from the similarity of the functions of organs, differently arranged. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. ... ... Dictionary of foreign words of the Russian language

- (from the Greek homologfa correspondence, agreement), the correspondence of organs in organisms of different species, due to their phylogenetic. kinship. Primary morphological the similarity of homologous organs can be, to one degree or another, secondarily obscured ... ... Biological encyclopedic dictionary

Similarity, transformation Dictionary of Russian synonyms. homology noun, number of synonyms: 3 polyhomology (1) ... Synonym dictionary

homology- and, w. homologie, it. homologie c. homologia consent. The similarity of organs having a general structure scheme, developing from similar primordia, but performing different functions in different species of animals or plants. Krysin 1998. Lex. Berezin ... ... Historical Dictionary of Russian Gallicisms

HOMOLOGY, the similarity of the main structures and organs of organisms, based on a common genetic inheritance. This often applies to organs that now have different appearance and function in different organisms. For example, despite the appearance ... Scientific and technical encyclopedic dictionary

1. The similarity in different organisms of organs of the same origin, developing from the same primordia and exhibiting the same morphological structure. 2. Geometric concept that expands the theory of symmetry to lov. Unambiguous ... ... Geological encyclopedia

homology- Substances with identical properties Topics of biotechnology EN homology ... Technical translator's guide

- (other Greek ὅμοιος similar, similar; λογος word, law) ... Wikipedia

I Homology (Greek homologia correspondence) (biological), the similarity of organs built according to the same plan and developing from the same primordia in different animals and plants; such Homologous organs may not be the same in appearance ... ... Great Soviet Encyclopedia

Books

• A set of tables. Chemistry. 8-9 grade (20 tables),. Educational album of 20 sheets. Valence. Atomic structure, Isotopes. Electronic configurations of atoms. Formation of covalent and ionic chemical bonds. Types of crystal lattices. ...