This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What is Homology?
Homology is a broad term used in biology to indicate similarity between multiple things. This similarity could be in structure of location. In evolutionary biology, homology is used for structure and anatomical position but not always functionality [1]. The figure above showing forelimbs is a great demonstration of homology across multiple organisms (Fig 1). While the figure shows forelimb homology, the same principle can be applied to genes and proteins. Homology can be broken down into orthologs and paralogs. Orthologs are genes in different species that generally have the same function [2] while paralogs develop from duplication and do not have the same function [2].
LXRA homologs in common organisms
The human LXRA gene has homologs with many species. These homologs are likely to have the same function in organisms with greater identity.
Homo sapiens
(Human) |
Pan troglodytes
(Common Chimpanzee) |
Mus Musculus
(Mouse) |
Rattus norvegicus
(Rat) |
Canis lupus familiaris
(Dog) |
Danio rerio
(Zebrafish) |
Drosophila melanogaster
(Fruit Fly) |
Caenorhabditis elegans
(Nematode) |
Discussion
As species diverge more and more through evolution it is expected that the conservation of genes decreases. This is shown by the percent identity to the human LXRA gene. The percent identity of mammalian organisms is 90% or above, indicating that the LXRA gene is highly conserved between these organisms. As species are evolutionarily distant the precent identity decreases. This can be seen in the Fruit Fly and C. elegans which have 40% or below identity.
References:
[1] Homology. (n.d.). Retrieved March 08, 2018, from https://www.biology-online.org/dictionary/Homology
[2] Chris Lewis at the U of S. (n.d.). Retrieved March 08, 2018, from http://homepage.usask.ca/~ctl271/857/def_homolog.shtml
[1] Homology. (n.d.). Retrieved March 08, 2018, from https://www.biology-online.org/dictionary/Homology
[2] Chris Lewis at the U of S. (n.d.). Retrieved March 08, 2018, from http://homepage.usask.ca/~ctl271/857/def_homolog.shtml