Homology (biology)

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The principle of homology: The biological relationships (shown by colours) of the bones in the forelimbs of vertebrates were used by Charles Darwin as an argument in favor of evolution.

In

adapted to different purposes as the result of descent with modification from a common ancestor. The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this, from Aristotle onwards, and it was explicitly analysed by Pierre Belon
in 1555.

In

testicles of mammals including humans. [citation needed
]

DNA sequences is similarly defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either a speciation event (orthologs) or a duplication event (paralogs). Homology among proteins or DNA is inferred from their sequence similarity. Significant similarity is strong evidence that two sequences are related by divergent evolution from a common ancestor. Alignments
of multiple sequences are used to discover the homologous regions.

Homology remains controversial in

primates
.

History

Pierre Belon systematically compared the skeletons of birds and humans in his Book of Birds (1555)[1]

Homology was noticed by

von Baer's laws in 1828, noting that related animals begin their development as similar embryos and then diverge: thus, animals in the same family are more closely related and diverge later than animals which are only in the same order and have fewer homologies. Von Baer's theory recognises that each taxon (such as a family) has distinctive shared features, and that embryonic development parallels the taxonomic hierarchy: not the same as recapitulation theory.[3] The term "homology" was first used in biology by the anatomist Richard Owen in 1843 when studying the similarities of vertebrate fins and limbs, defining it as the "same organ in different animals under every variety of form and function",[6] and contrasting it with the matching term "analogy" which he used to describe different structures with the same function. Owen codified 3 main criteria for determining if features were homologous: position, development, and composition. In 1859, Charles Darwin explained homologous structures as meaning that the organisms concerned shared a body plan from a common ancestor, and that taxa were branches of a single tree of life.[2][7][3]

Definition

halteres
.
The two pairs of wings of ancestral insects are represented by homologous structures in modern insects — elytra, wings, and halteres.

The word homology, coined in about 1656, is derived from the Greek ὁμόλογος homologos from ὁμός homos 'same' and λόγος logos 'relation'.[8][9][a]

Similar biological structures or sequences in different

Dipteran flies the second pair of wings has evolved into small halteres used for balance.[b][13]

Similarly, the forelimbs of ancestral

lobe-finned fish such as Eusthenopteron.[14]

Homology vs. analogy

analogous
but not homologous to an insect's wings.
Further information: Convergent evolution

The opposite of homologous organs are analogous organs which do similar jobs in two taxa that were not

bat wings are analogous as wings, but homologous as forelimbs because the organ served as a forearm (not a wing) in the last common ancestor of tetrapods, and evolved in different ways in the three groups. Thus, in the pterosaurs, the "wing" involves both the forelimb and the hindlimb.[17] Analogy is called homoplasy in cladistics, and convergent or parallel evolution in evolutionary biology.[18][19]

In cladistics

Further information: Cladistics

Specialised terms are used in taxonomic research. Primary homology is a researcher's initial hypothesis based on similar structure or anatomical connections, suggesting that a character state in two or more taxa share is shared due to common ancestry. Primary homology may be conceptually broken down further: we may consider all of the states of the same character as "homologous" parts of a single, unspecified, transformation series. This has been referred to as topographical correspondence. For example, in an aligned DNA sequence matrix, all of the A, G, C, T or implied gaps at a given nucleotide site are homologous in this way. Character state identity is the hypothesis that the particular condition in two or more taxa is "the same" as far as our character coding scheme is concerned. Thus, two Adenines at the same aligned nucleotide site are hypothesized to be homologous unless that hypothesis is subsequently contradicted by other evidence. Secondary homology is implied by

synapomorphy, a shared derived character or trait state that distinguishes a clade from other organisms.[22][23][24]

Shared ancestral character states, symplesiomorphies, represent either synapomorphies of a more inclusive group, or complementary states (often absences) that unite no natural group of organisms. For example, the presence of wings is a synapomorphy for pterygote insects, but a symplesiomorphy for holometabolous insects. Absence of wings in non-pterygote insects and other organisms is a complementary symplesiomorphy that unites no group (for example, absence of wings provides no evidence of common ancestry of silverfish, spiders and annelid worms). On the other hand, absence (or secondary loss) of wings is a synapomorphy for fleas. Patterns such as these lead many cladists to consider the concept of homology and the concept of synapomorphy to be equivalent.[25][24] Some cladists follow the pre-cladistic definition of homology of Haas and Simpson,[26] and view both synapomorphies and symplesiomorphies as homologous character states.[27]

In different taxa

pax6
alterations result in similar changes to eye morphology and function across a wide range of taxa.

Homologies provide the fundamental basis for all biological classification, although some may be highly counter-intuitive. For example,

pax6 genes that control the development of the eyes of vertebrates and arthropods were unexpected, as the organs are anatomically dissimilar and appeared to have evolved entirely independently.[28][29]

In arthropods

Further information: Arthropod leg

The embryonic body segments (somites) of different arthropod taxa have diverged from a simple body plan with many similar appendages which are serially homologous, into a variety of body plans with fewer segments equipped with specialised appendages.[30] The homologies between these have been discovered by comparing genes in evolutionary developmental biology.[28]

Hox genes in arthropod segmentation
Somite
(body
segment)
Trilobitomorpha)
 Spider
(Chelicerata)
 Centipede
(Myriapoda)
 Insect
(Hexapoda)
Crustacea)
1 antennae chelicerae (jaws and fangs) antennae antennae 1st antennae
2 1st legs
pedipalps
 - - 2nd antennae
3 2nd legs 1st legs mandibles mandibles mandibles (jaws)
4 3rd legs 2nd legs 1st maxillae 1st maxillae 1st maxillae
5 4th legs 3rd legs 2nd maxillae 2nd maxillae 2nd maxillae
6 5th legs 4th legs collum (no legs) 1st legs 1st legs
7 6th legs - 1st legs 2nd legs 2nd legs
8 7th legs - 2nd legs 3rd legs 3rd legs
9 8th legs - 3rd legs - 4th legs
10 9th legs - 4th legs - 5th legs

Among insects, the stinger of the female honey bee is a modified ovipositor, homologous with ovipositors in other insects such as the Orthoptera, Hemiptera, and those Hymenoptera without stingers.[31]

In mammals

Further information: Comparative anatomy

The three small bones in the middle ear of mammals including humans, the malleus, incus, and stapes, are today used to transmit sound from the eardrum to the inner ear. The malleus and incus develop in the embryo from structures that form jaw bones (the quadrate and the articular) in lizards, and in fossils of lizard-like ancestors of mammals. Both lines of evidence show that these bones are homologous, sharing a common ancestor.[32]

Among the many homologies in mammal reproductive systems, ovaries and testicles are homologous.[33]

Rudimentary organs such as the human tailbone, now much reduced from their functional state, are readily understood as signs of evolution, the explanation being that they were cut down by natural selection from functioning organs when their functions were no longer needed, but make no sense at all if species are considered to be fixed. The tailbone is homologous to the tails of other primates.[34]

In plants

Leaves, stems, and roots

In many plants, defensive or storage structures are made by modifications of the development of primary

pitcher plants, the insect-trapping jaws of Venus flytrap, and the spines of cactuses, all homologous.[35]

Primary organs Defensive structures Storage structures
Leaves Spines Swollen leaves (e.g.
succulents
)
Stems Thorns Tubers (e.g. potato), rhizomes (e.g. ginger), fleshy stems (e.g. cacti)
Roots - Root tubers (e.g. sweet potato), taproot (e.g. carrot)

Certain

compound leaves of flowering plants are partially homologous both to leaves and shoots, because their development has evolved from a genetic mosaic of leaf and shoot development.[36][37]

Flower parts

carpels. In two specific whorls of the floral meristem
, each class of organ identity genes is switched on.
Further information: ABC model of flower development

The four types of flower parts, namely

Goethe correctly noted in 1790. The development of these parts through a pattern of gene expression in the growing zones (meristems) is described by the ABC model of flower development. Each of the four types of flower parts is serially repeated in concentric whorls, controlled by a small number of genes acting in various combinations. Thus, A genes working alone result in sepal formation; A and B together produce petals; B and C together create stamens; C alone produces carpels. When none of the genes are active, leaves are formed. Two more groups of genes, D to form ovules and E for the floral whorls, complete the model. The genes are evidently ancient, as old as the flowering plants themselves.[4]

Developmental biology

The Cretaceous snake Eupodophis had hind legs (circled).

calcaneum, astragalus) as in tetrapods with legs today.[38]

Sequence homology

Main article: Sequence homology
Further information: Deep homology and Evolutionary developmental biology
conservative, semi-conservative, and non-conservative amino acid replacements are indicated.[39]

As with anatomical structures,

DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either a speciation event (orthologs) or a duplication event (paralogs). Homology among proteins or DNA is typically inferred from their sequence similarity. Significant similarity is strong evidence that two sequences are related by divergent evolution of a common ancestor. Alignments of multiple sequences are used to indicate which regions of each sequence are homologous.[40]

Homologous sequences are orthologous if they are descended from the same ancestral sequence separated by a speciation event: when a species diverges into two separate species, the copies of a single gene in the two resulting species are said to be orthologous. The term "ortholog" was coined in 1970 by the molecular evolutionist Walter Fitch.[41]

Homologous sequences are paralogous if they were created by a duplication event within the genome. For gene duplication events, if a gene in an organism is duplicated, the two copies are paralogous. They can shape the structure of whole genomes and thus explain genome evolution to a large extent. Examples include the Homeobox (Hox) genes in animals. These genes not only underwent gene duplications within chromosomes but also whole genome duplications. As a result, Hox genes in most vertebrates are spread across multiple chromosomes: the HoxA–D clusters are the best studied.[42]

Some sequences are homologous, but they have diverged so much that their sequence similarity is not sufficient to establish homology. However, many proteins have retained very similar structures, and structural alignment can be used to demonstrate their homology.[43]

primates
.

In behaviour

Main article: Homology (psychology)

It has been suggested that some

dominance hierarchies are homologous across the primates.[45]

As with morphological features or DNA, shared similarity in behavior provides evidence for common ancestry.[46] The hypothesis that a behavioral character is not homologous should be based on an incongruent distribution of that character with respect to other features that are presumed to reflect the true pattern of relationships. This is an application of Willi Hennig's[47] auxiliary principle.

Notes

  1. homogeneous" which refers to the uniformity of a mixture.[10][11]
  2. ^ If the two pairs of wings are considered as interchangeable, homologous structures, this may be described as a parallel reduction in the number of wings, but otherwise the two changes are each divergent changes in one pair of wings.
  3. ^ These are coloured in the lead image: humerus brown, radius pale buff, ulna red.

References

  1. ^
    PMID 10332750
    .
  2. ^
    PMID 10332750. {{cite book}}: |journal= ignored (help
    )
  3. ^ a b c d Brigandt, Ingo (23 November 2011). "Essay: Homology". The Embryo Project Encyclopedia.
  4. ^
    doi:10.1590/S1677-04202005000400001
    .
  5. ^ Geoffroy Saint-Hilaire, Etienne (1818). Philosophie anatomique. Vol. 1: Des organes respiratoires sous le rapport de la détermination et de l'identité de leurs piecès osseuses. Vol. 1. Paris: J. B. Baillière.
  6. ^ Owen, Richard (1843). Lectures on the Comparative Anatomy and Physiology of the Invertebrate Animals, Delivered at the Royal College of Surgeons in 1843. Longman, Brown, Green, and Longmans. pp. 374, 379.
  7. PMID 18536034
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  8. ^ Bower, Frederick Orpen (1906). "Plant Morphology". Congress of Arts and Science: Universal Exposition, St. Louis, 1904. Houghton, Mifflin. p. 64.
  9. ISBN 978-0-415-28032-7
    .
  10. ^ "homogeneous, adj.". OED Online. March 2016. Oxford University Press. http://www.oed.com/view/Entry/88045? (accessed April 09, 2016).
  11. ^ "homogenous, adj.". OED Online. March 2016. Oxford University Press. http://www.oed.com/view/Entry/88055? (accessed April 09, 2016).
  12. ISBN 978-1-4008-5146-1
    . elytra have very little similarity with typical wings, but are clearly homologous to forewings. Hence butterflies, flies, and beetles all have two pairs of dorsal appendages that are homologous among species.
  13. ISBN 978-1-4419-8981-9
    . For example, wing and haltere are homologous, yet widely divergent, organs that normally arise as dorsal appendages of the second thoracic (T2) and third thoracic (T3) segments, respectively.
  14. ^ "Homology: Legs and Limbs". UC Berkeley. Retrieved 15 December 2016.
  15. ^ "Secret Found to Flight of 'Helicopter Seeds'". LiveScience. 11 June 2009. Retrieved 2 March 2017.
  16. S2CID 12216605
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  17. S2CID 205469918
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  18. ^ Cf. Butler, A. B.: Homology and Homoplasty. In: Squire, Larry R. (Ed.): Encyclopedia of Neuroscience, Academic Press, 2009, pp. 1195–1199.
  19. ^ "Homologous structure vs. analogous structure: What is the difference?". Retrieved 27 September 2016.
  20. S2CID 3551391
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  21. S2CID 85385271
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  22. ISBN 978-1-4443-1336-9
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  23. S2CID 86806203
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  24. ^
    S2CID 221550586
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  25. ^ Patterson, C. (1982). "Morphological characters and homology". In K. A. Joysey; A. E. Friday (eds.). Problems of Phylogenetic Reconstruction. London and New York: Academic Press. pp. 21–74.
  26. ^ Haas, O. and G. G. Simpson. 1946. Analysis of some phylogenetic terms, with attempts at redefinition. Proc. Amer. Phil. Soc. 90:319-349.
  27. S2CID 221582887
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  28. ^ a b Brusca, R. C.; Brusca, G. J. (1990). Invertebrates. Sinauer Associates. p. 669.
  29. ISBN 978-0-297-85094-6
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  30. ISBN 978-0-470-51566-2
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  31. doi:10.1051/apido:19820301
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  32. ^ "Homology: From jaws to ears — an unusual example of a homology". UC Berkeley. Retrieved 15 December 2016.
  33. ISBN 978-0-07-338282-1
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  34. ISBN 978-0-679-64288-6
    .
  35. ^ "Homology: Leave it to the plants". University of California at Berkeley. Retrieved 7 May 2017.
  36. JSTOR 2418787
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  37. ISBN 978-0-12-319583-8
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  38. ^ "Homologies: developmental biology". UC Berkeley. Retrieved 15 December 2016.
  39. ^ "Clustal FAQ #Symbols". Clustal. Archived from the original on 24 October 2016. Retrieved 8 December 2014.
  40. PMID 16285863
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  41. PMID 5449325
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  42. PMID 17644373
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  43. PMID 36419248
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  44. PMID 22711075
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  45. ISBN 978-1-135-83123-3. Finally, much recent information on children's and nonhuman primates' behavior in groups, a conjunction of hard human data and hard nonhuman primate data, lends credence to our comparison. Our conclusion is that, based on their agreement in several unusual characteristics, dominance patterns are homologous in primates. This agreement of unusual characteristics is found at several levels, including fine motor movement, gross motor movement, and behavior at the group level. {{cite book}}: |work= ignored (help
    )
  46. ^ Wenzel, John W. 1992. Behavioral homology and phylogeny. Annual Review of Ecology and Systematics 23:361-381
  47. ^ Hennig, W. 1966. Phylogenetic Systematics. University of Illinois Press

Further reading

External links

  • Media related to Homology at Wikimedia Commons

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