This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What is homology?
Homology in biology refers to similarities in traits among different species because of common ancestry. [1] Interestingly, the concept of homology predates Darwin's "On the Origin of Species" and, although it has been a central idea in the field of comparative biology, the criteria of its application has remained controversial. [1] Features of different organisms that have similar structure are considered homologous if they have a common evolutionary origin, even if their function differs between the organisms. [2] Conversely, features that have similar function between organisms but completely different evolutionary origin are considered analogous. [2]
In genetics, two genes in two separate organisms are considered homologous if they are derived from the same gene in a common ancestor. [3] This can be measured by comparing protein and DNA sequences using bioinformatics tools such as NCBI's Basic Local Alignment Search Tool (BLAST) and viewing the sequence similarity or identity.
StAR Common Homologs
Human
Homo sapiens |
Rhesus macaque
Macaca mulatta STAR
Accession number: NP_001252698.1 Length: 285aa Identity: 97.19% Western clawed frog
Xenopus tropicalis STAR
Accession number: XP_002932770.1 Length: 285aa Identity: 69.12% |
Brown rat
Rattus norvegicus STAR
Accession number: NP_113746.1 Length: 284aa Identity: 87.72% Zebrafish
Danio rerio STAR
Accession number: NP_571738.1 Length: 285aa Identity: 64.62% |
House mouse
Mus musculus STAR
Accession number: NP_035615.2 Length: 284aa Identity: 87.02% Roundworm
Caenorhabditis elegans STRL-1
Accession number: NP_001251251.1 Length: 241aa Identity: 27.68% |
Conclusion
The StAR protein sequence is most highly conserved among mammals, however, with identities of 69% and 65% for the western clawed frog and zebrafish, respectively, the sequence is also pretty highly conserved. This suggests that StAR may play a similarly important role in these homologs. The roundworm, with an identity of only 28% is not nearly as good as the rest of the homologs, it would be interesting to explore what role the StAR-like homolog, STRL-1, plays in C. elegans compared to that of the rest of the homologs.
References
[1] Sommer, R. J. (2008). Homology and the hierarchy of biological systems. BioEssay. 30(7):653-658.
[2] Albert.io. team “Difference Between Homologous and Analogous Structures.” Albert Blog, 3 Apr. 2017, www.albert.io/blog/difference-between-homologous-and-analogous-structures/.
[3] Wagner, G. P. (2007). The developmental genetics of homology. Nature Reviews Genetics. 8:473-479.
[1] Sommer, R. J. (2008). Homology and the hierarchy of biological systems. BioEssay. 30(7):653-658.
[2] Albert.io. team “Difference Between Homologous and Analogous Structures.” Albert Blog, 3 Apr. 2017, www.albert.io/blog/difference-between-homologous-and-analogous-structures/.
[3] Wagner, G. P. (2007). The developmental genetics of homology. Nature Reviews Genetics. 8:473-479.
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