Homologous chromosome
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Reverted edits by [[Special:Contributions/67.34.117.112|67.34.117.112]] ([[User talk:67.34.117.112|talk]]) to last version by 69.150.243.254
'''Homologous chromosomes''' are [[chromosomes]] in a [[biological cell]] that pair ([[synapsis|synapse]]) during [[meiosis]], or alternatively, non-identical chromosomes that contain information for the same biological features and contain the same [[gene]]s at the same [[locus (genetics)|loci]] but possibly different genetic information, called [[allele]]s, at those genes. For example, two chromosomes may have genes encoding eye color, but one may code for brown eyes, the other for blue.
Non-homologous chromosomes representing all the biological features of an organism form a set, and the number of sets in a cell is called [[ploidy]]. In [[diploid]] organisms (most plants and animals), each homologous chromosome is [[biological inheritance|inherited]] from a different [[parent]]. But [[polyploid]] organisms have more than two homologous chromosomes.
Homologous chromosomes are similar in length, except for [[sex chromosome]]s in several [[taxa]], where the [[X chromosome]] is considerably larger than the [[Y chromosome]]. These chromosomes share only small regions of [[homology (biology)|homology]].
Humans have 22 pairs of homologous non-sex chromosomes (called [[autosomes]]). Each member of a pair is inherited from one of their two parents. In addition, female humans have a homologous pair of [[sex chromosomes]] ([[X chromosome|2 X's]]); males have an [[X chromosome|X]] and a [[Y chromosome]].
Homologous chromosomes are two pairs of sister,and brothers chromatids that have gone through the process of crossing over and meiosis. In this process the homologous chromosomes cross over (not the sister chromatids)each other and exchange genetic information. This causes each final cell of meiosis to have genetic information from both parents. It also causes genetic variation, but that is a different topic.The homologous chromosomes are similar in length.
== Other terms ==
Homologous chromosomes are not to be confused with [[sister chromatid]]s, the identical chromosomes that separate during [[mitosis]] or [[meiosis|meiosis II]].
Homology of chromosomes is different than ''[[Homology (biology)#homology of sequences in genetics|homology of genetic sequences]]'', and predates that use of the term ''homology''. An exception arises with [[allopolyploidy]] where chromosomes pair up by age, so sequence similarity is used to determine the original chromosomal sets.
Homologous chromosomes are also very similar to, and often confused with the term [[synteny]] (or gene homology)—which refers to genes located on the same section of chromosome between individuals of the same or different species.
==External links==
* [http://www.ncbi.nlm.nih.gov/Homology/ Comparative Maps] NIH's National Library of Medicine NCBI link to Gene Homology resources, and Comparative Chromosome Maps of the Human, Mouse, and Rat.
* [http://www.ncbi.nlm.nih.gov/ NCBI Home Page] NIH's National Library of Medicine NCBI (National Center for Biotechnology Information) link to a tremendous number of resources.
See also a link from the [[synteny]] definition:
* [http://cinteny.cchmc.org/ Synteny server] Server for Synteny Identification and Analysis of Genome Rearrangement—the Identification of synteny and calculating reversal distances.
[[Category:Cytogenetics]]
[[da:Homologe kromosomer]]
[[es:Cromosoma homólogo]]
[[fr:Chromosomes homologues]]
[[he:כרומוזום הומולוגי]]
[[pl:Chromosomy homologiczne]]
[[pt:Cromossomos homólogos]]
[[sr:хомологи хромозоми]]
[[Category:Genetics]]
[[da:Homologe kromosomer]]
[[es:Cromosoma homólogo]]
[[fr:Chromosomes homologues]]
[[he:כרומוזום הומולוגי]]
[[pl:Chromosomy homologiczne]]
[[pt:Cromossomos homólogos]]
[[sr:хомологи хромозоми]]