Changes

==Origin==

==Origin==

[[Greek]] homologos [[agree]]ing, from hom- + legein to say

[[Greek]] homologos [[agree]]ing, from hom- + legein to say

*[http://en.wikipedia.org/wiki/17th_century 1660]

*[https://en.wikipedia.org/wiki/17th_century 1660]

==Definitions==

==Definitions==

*1a : having the same [[relative]] position, [[value]], or [[structure]]: as (1) : exhibiting biological homology (2) : having the same or allelic genes with genetic loci usually arranged in the same order <homologous chromosomes>  

*1a : having the same [[relative]] position, [[value]], or [[structure]]: as (1) : exhibiting biological homology (2) : having the same or allelic genes with genetic loci usually arranged in the same order <homologous chromosomes>  

*2: derived from or [[developed]] in [[response]] to [[organisms]] of the same species  

*2: derived from or [[developed]] in [[response]] to [[organisms]] of the same species  

==Description==

==Description==

A '''homologous''' trait is any characteristic of [[organisms]] that is derived from a common [[ancestor]]. This is [[contrasted]] to [[analogous]] traits: similarities between [[organisms]] that were not in the last common [[ancestor]] of the taxa being considered but rather [http://en.wikipedia.org/wiki/Convergent_evolution evolved separately]. As defined by Owen, a homology is a "[[structural]] [[correspondence]]", whereas an [[analogy]] is a "non-correspondent similarity".

A '''homologous''' trait is any characteristic of [[organisms]] that is derived from a common [[ancestor]]. This is [[contrasted]] to [[analogous]] traits: similarities between [[organisms]] that were not in the last common [[ancestor]] of the taxa being considered but rather [https://en.wikipedia.org/wiki/Convergent_evolution evolved separately]. As defined by Owen, a homology is a "[[structural]] [[correspondence]]", whereas an [[analogy]] is a "non-correspondent similarity".

Whether or not a trait is homologous depends on both the taxonomic and anatomical level at which the trait is [[examined]]. For example, the bird and [http://en.wikipedia.org/wiki/Bat_wing bat wing] are homologous as forearms in [http://en.wikipedia.org/wiki/Tetrapod tetrapods]. However, they are not homologous as wings, because the organ served as a forearm (not a wing) in the last [http://en.wikipedia.org/wiki/Common_descent common ancestor] of tetrapods. By definition, any homologous trait defines a [http://en.wikipedia.org/wiki/Clade clade]—a [http://en.wikipedia.org/wiki/Monophyly monophyletic] [http://en.wikipedia.org/wiki/Taxon taxon] in which all the members have the trait (or have lost it secondarily); and all non-members lack it.

Whether or not a trait is homologous depends on both the taxonomic and anatomical level at which the trait is [[examined]]. For example, the bird and [https://en.wikipedia.org/wiki/Bat_wing bat wing] are homologous as forearms in [https://en.wikipedia.org/wiki/Tetrapod tetrapods]. However, they are not homologous as wings, because the organ served as a forearm (not a wing) in the last [https://en.wikipedia.org/wiki/Common_descent common ancestor] of tetrapods. By definition, any homologous trait defines a [https://en.wikipedia.org/wiki/Clade clade]—a [https://en.wikipedia.org/wiki/Monophyly monophyletic] [https://en.wikipedia.org/wiki/Taxon taxon] in which all the members have the trait (or have lost it secondarily); and all non-members lack it.

A homologous trait may be homoplasious – that is, it has evolved [[independently]], but from the same [[ancestral]] [[structure]] – plesiomorphic – that is, present in a common ancestor but secondarily lost in some of its descendants – or (syn)apomorphic – present in an ancestor and all of its descendants.[1]

A homologous trait may be homoplasious – that is, it has evolved [[independently]], but from the same [[ancestral]] [[structure]] – plesiomorphic – that is, present in a common ancestor but secondarily lost in some of its descendants – or (syn)apomorphic – present in an ancestor and all of its descendants.[1]

A homologous trait is often called a '''homolog''' (also spelled homologue). In [[genetics]], the term "homolog" is used both to refer to a homologous [[protein]], and to the gene ([[DNA]] sequence) encoding it.[http://en.wikipedia.org/wiki/Homology_(biology)]

A homologous trait is often called a '''homolog''' (also spelled homologue). In [[genetics]], the term "homolog" is used both to refer to a homologous [[protein]], and to the gene ([[DNA]] sequence) encoding it.[https://en.wikipedia.org/wiki/Homology_(biology)]

[[Category: Biology]]

[[Category: Biology]]