What is homology?
Homology can be defined as a degree of similarity in a position or structure that indicates a common origin [1]. Biologists often analyze different organisms with a known common ancestor, and determine homology based on physical features. In Figure 1, the bones of different mammals can be compared; all have the same bones but are different in size, shape, and potentially function. This differs greatly from analogy, which is the similarity in structure and function of a given trait, but the two organisms do not share a common ancestor [1].
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In genetics, homology is measured by comparing protein or DNA sequences. Also, homologous genes share a high sequence identity or similarity [2]. Sequence homology can indicate both homologs share a common ancestor as well as give insight to a common function. Orthologs are homologous sequences in which any genes in different species that are similar to each other and originated from a common ancestor, regardless of function. Paralogs are homologous sequences which were separated by a gene duplication event. Paralogs typically have the same or similar function [2].
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Cln3 Homologs in Common Organisms
Homo sapiens
(Human)
(Human)
Xenopus tropicalis
(Western Clawed Frog) |
Drosophila melanogaster
(Fruit Fly) |
Gallus gallus
(Chicken) |
Octopoda
(Octopus) |
Mus musculus
(Mouse) |
Canis lupus familiaris
(Dog) |
|
|
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Caenorhabditis elegans
(Nematode) |
Danio rerio
(Zebrafish) |
Conclusion
Scientists study evolutionary biology to find homologous organisms/chromosomes for their organism of interest. Using homologous organisms, one can detect the most recent common ancestor as well as infer potential functions of the given trait. As evolution continues, organisms will continuously develop traits and mutations that lower their percent of common identity. Thus far, the CLN3 protein is still highly conserved across numerous model organisms. This will likely remain constant, because a signature symptom of Batten Disease is retinal degeneration as well as the buildup of byproducts from organelles in neurons. Comparing the conservation of the gene and the physiology of the homologs is very valuable in research by aiding scientists to understand the complexity of the gene's function.
References:
[1] Customers. (2014, May 12). Homology. Retrieved from https://www.biology-online.org/dictionary/Homology
[2]Homology (biology). (n.d.). Retrieved from http://www.newworldencyclopedia.org/entry/Homology_(biology)
Header: https://twitter.com/failunfailunm/status/1007257830813061122
Figure 1: https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/10.22/
Figure 2: https://ivoiregion.net/
[2]Homology (biology). (n.d.). Retrieved from http://www.newworldencyclopedia.org/entry/Homology_(biology)
Header: https://twitter.com/failunfailunm/status/1007257830813061122
Figure 1: https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/10.22/
Figure 2: https://ivoiregion.net/
This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.