This page was produced as an assignment for Genetics 564, an undergraduate capstone course at The University of Wisconsin - Madison.
What is Homology?
How can the same genes, proteins, and even structures be found in different species? Across different organisms, various structures may have different functions but are derived from common ancestors. Similar characteristics due to relatedness are known as homologies [1].
The Central Dogma
Just as bones and other and other structures can be homologs, so can genes that code for proteins. Consider the Central Dogma of Biology - DNA is a universal coding sequence for genetic information information including different kinds of proteins across all living organisms. The double stranded DNA in the genome is transcribed into single stranded RNA, which is translated into a sequence of amino acids. The amino acids then interact with each other to fold into proteins (Fig. 2). The sharing of genes for proteins across different organisms works in the same way for sharing similar bone structures in different organisms. Therefore we know that if two organisms contain similar genes, they have similar proteins.
The human gene that codes for Amyloid Precursor Protein (APP) is found in many different species. Its conservation throughout organisms is likely due to APP's role in the central nervous system.
Homo Sapien
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Mus musculus
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Pan troglodytes
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Rattus norvegicusDanio rerio |
Caenorhabditis elegansSus scrofaOryctolagus cuniculus |
Gallus gallusCaenorhabditis elegansDrosophila melogasterFruit Fly
Amyloid precursor protein-like (Appl) - RB Accession Number: NP_001245448 Length: 890 AA 22.86% Identity |
Discussion
When two protein homologs have a higher percent identity, they are considered to have shared characteristics. APP is very well conserved across mammals and even has homologs in fish, birds, and invertebrates. This information will be very important when selecting a model organism for the Specific Aims.
References
Images:
Figure 1. http://www.bio.miami.edu/dana/160/160S13_5.html
Figure 2. http://bptba.lipi.go.id/
Figure 3. https://en.wikipedia.org/wiki/Amyloid_precursor_protein
[1] Caldwell, R, et al. 2008. Understanding Evolution: Homologies. University of California Museum of Paleontology. Available from evolution.berkeley.edu/evolibrary/article/lines_04
Figure 1. http://www.bio.miami.edu/dana/160/160S13_5.html
Figure 2. http://bptba.lipi.go.id/
Figure 3. https://en.wikipedia.org/wiki/Amyloid_precursor_protein
[1] Caldwell, R, et al. 2008. Understanding Evolution: Homologies. University of California Museum of Paleontology. Available from evolution.berkeley.edu/evolibrary/article/lines_04