This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What is Homology?
Genes are conserved across species. A gene in any given species most likely has a homolog in another species. That means that the gene that codes for that protein is very similar to the gene that codes for that same protein in a different species.
Lets use our gene, TGFB1, as an example. Humans have a copy of the TGFB1 gene in their genome, which encodes for the TGFB1 protein. In addition, mice have a TGFB1 gene which produces a TGFB1 protein very similar to ours. These two TGFB1 proteins would be refered to as homologs. The ability to study the effects of TGFB1 in mice opens a wide array of possibilities.
Because we use mice to model for TGFB1, we can describe the mouse as a good model organism. A model organism is exactly what it sounds like, an animal model for a disease or mutation that allows us to learn more about our own biology and physiology. The type of homolog that crosses species through evolution in this way is called an ortholog. To learn more about the applications of orthologs, visit the phylogeny page!
Lets use our gene, TGFB1, as an example. Humans have a copy of the TGFB1 gene in their genome, which encodes for the TGFB1 protein. In addition, mice have a TGFB1 gene which produces a TGFB1 protein very similar to ours. These two TGFB1 proteins would be refered to as homologs. The ability to study the effects of TGFB1 in mice opens a wide array of possibilities.
Because we use mice to model for TGFB1, we can describe the mouse as a good model organism. A model organism is exactly what it sounds like, an animal model for a disease or mutation that allows us to learn more about our own biology and physiology. The type of homolog that crosses species through evolution in this way is called an ortholog. To learn more about the applications of orthologs, visit the phylogeny page!
What is a pre-pro-protein?
Many proteins are coded for in the genome as something called a pre-protein. To learn more about a protein, read the 'What is a protein' section on the phylogenetics page
Pre-protein signifies the fact that the protein is translated with a physical part that keeps it inactive until necessary. The part of the pre-protein that is cleaved is called the propeptide domain. In the case of the TGFB1 preprotein, the latency associated peptide is removed so that the TGFB1 can become functional. TGFB1 has both a propeptide domain and the active TGFB1 domain. The propeptide domain is cleaved off before excretion and activity of TGFB1 |
TGFB1 Homologs
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Analysis
The TGFB1 protein is conserved with fairly high percent identity throughout the species listed above. Percent identity is a measure of how similar the homologous protein is to the human protein. We can expect that the more closely related the species is to humans, the higher the percent identity. Chimpanzees for example share a 100% identity with the human TGFB1 protein. Fruit flies, drosophila, share only a 23% identity. Because TGFB1 is such a widely used protein in several different signaling functions throughout growth and development, it is useful to compare species of both high and low percent identities. Using species with immune systems extremely different from ours, like the fruit fly, we can compare and contrast the regions of the protein that are similar and dissimilar to our own and to species who have immune systems like ours. Through this comparison we can identify the more conserved regions between animals of similar immune systems, and hypothesize that these areas are the regions of TGFB1 that may be important to immune function.
References
[1] Preproprotein. (2017, March 17). Retrieved April 30, 2017, from http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100343450
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[1] Edited from: http://www.memphisanimalclinic.com/pet-health/general-health-concerns/allergies/
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[1] Edited from: http://www.memphisanimalclinic.com/pet-health/general-health-concerns/allergies/