This web page was produced as an assignment for Genetics 564, an undergraduate capstone course at UW-Madison.
What is Homology?
Homology is the idea that animals that are related will share similar characteristics due to their shared ancestry. This leads to conservation of certain characteristics throughout many organisms. For example, the animals in the picture all have different limbs ranging from wings to find to hooves. However, the underlying bone structure is identical in all of these animals. This conservation of bone structure suggests that all of these animals are derived from a common ancestor that first developed this bone structure. [1]
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How Can Homology Be Applied to Genetics?
The concept of homology can also be applied to genetics. Organisms that are related have biological sequences in common that were passed down from a common ancestor. Conserved sequences are generally conserved because they are important for healthy functioning; this feature makes them a good target for studying disease. [2]
There are two types of genetic homologs: Paralogs: Arise within one organism as a result of a gene duplication event. The genes generally have slightly different but related functions. [3] Orthologs: The same gene in different organisms. The function of the gene and its corresponding protein are generally conserved. [3] |
Homology in MTHFR
Xenopus Tropicalis (Tropical Clawed Frog)
MTHFR Accession Link: NP_001096464 643 Amino Acids 82% Identity |
Drosophila Melanogaster (Fruit Fly)
Uncharacterized Protein Accession Link: NP_648462.1 349 Amino Acids 28% Identity |
Discussion
MTHFR is a well-conserved gene with homologs in all common model organisms. This includes vertebrates, invertebrates, and plants. There is high percent identity in nearly all animals, especially vertebrates. Percent identity refers to the qualitative measurement of how similar two sequences are. Generally, there must be 30% identity shared between two genes for them to be considered homologous. [4] All animals reached this threshold except Drosophila melanogaster.
References:
[1] University of California Berkley. (n.d.) Homologies. Understanding Evolution. Retrieved from: https://evolution.berkeley.edu/evolibrary/article/lines_04
[2] University of California Berkley. (n.d.) Homologous Genes. Understanding Evolution. Retrieved from: https://evolution.berkeley.edu/evolibrary/article/1_0_0/eyes_10
[3] Koonin, E.V. Orthologs, paralogs, and evolutionary genomics. Annual Review of Genetics, 39, 309-338.
[4] Curr Protoc Bioinformatics. (2013). An introduction to sequence similarity ("homology") searching. HHS Public Access.
Images:
Header: http://bytesizebio.net/2009/07/15/distant-homology-and-being-a-little-pregnant/
Figure 1: https://biologywise.com/examples-of-homologous-structures
Figure 2: https://ivoiregion.net/
Human: http://www.thelockinmovie.com/human-silhouette-clip-art/
Mouse: https://www.shutterstock.com/search/mouse+silhouette?studio=1
Rat: https://www.shutterstock.com/search/rat+silhouette
Zebrafish: https://gtgc2016.sciencesconf.org/conference/gtgc2016/YvesClement_2016.07.01_GTGC.pdf
Frog: https://www.stockunlimited.com/vector-illustration/silhouette-of-frog_1446995.html
Fly: https://www.shutterstock.com/image-vector/insect-silhouettefly-musca-domestica-fly-silhouette-389917096
Roundworm: https://media.nature.com/original/nature-assets/nmeth/journal/v10/n7/extref/nmeth.2475-S1.pdf
Yeast: https://www.canstockphoto.com/illustration/cerevisiae.html
Fungus: https://www.benchfly.com/blog/the-almighty-fungi-the-revolutionary-neurospora-crassa/
Mustard Seed: http://blog.garnetcommunity.org.uk/arabidopsis-basics/
[1] University of California Berkley. (n.d.) Homologies. Understanding Evolution. Retrieved from: https://evolution.berkeley.edu/evolibrary/article/lines_04
[2] University of California Berkley. (n.d.) Homologous Genes. Understanding Evolution. Retrieved from: https://evolution.berkeley.edu/evolibrary/article/1_0_0/eyes_10
[3] Koonin, E.V. Orthologs, paralogs, and evolutionary genomics. Annual Review of Genetics, 39, 309-338.
[4] Curr Protoc Bioinformatics. (2013). An introduction to sequence similarity ("homology") searching. HHS Public Access.
Images:
Header: http://bytesizebio.net/2009/07/15/distant-homology-and-being-a-little-pregnant/
Figure 1: https://biologywise.com/examples-of-homologous-structures
Figure 2: https://ivoiregion.net/
Human: http://www.thelockinmovie.com/human-silhouette-clip-art/
Mouse: https://www.shutterstock.com/search/mouse+silhouette?studio=1
Rat: https://www.shutterstock.com/search/rat+silhouette
Zebrafish: https://gtgc2016.sciencesconf.org/conference/gtgc2016/YvesClement_2016.07.01_GTGC.pdf
Frog: https://www.stockunlimited.com/vector-illustration/silhouette-of-frog_1446995.html
Fly: https://www.shutterstock.com/image-vector/insect-silhouettefly-musca-domestica-fly-silhouette-389917096
Roundworm: https://media.nature.com/original/nature-assets/nmeth/journal/v10/n7/extref/nmeth.2475-S1.pdf
Yeast: https://www.canstockphoto.com/illustration/cerevisiae.html
Fungus: https://www.benchfly.com/blog/the-almighty-fungi-the-revolutionary-neurospora-crassa/
Mustard Seed: http://blog.garnetcommunity.org.uk/arabidopsis-basics/