Homology
This page was produced as an assignment for Genetics 564 an undergraduate capstone course at UW-Madison.
The concept of homology describes the shared ancestry between structures of organisms belonging to different taxa. As a classic example, the picture below depicts similar bone structures found in a bat wing, a whale flipper, and a human arm. The structures were present in a common ancestor in some ancient form, and as speciation events occurred and these species diverged from one another over time, these structures underwent different evolutionary pressures, resulting in slightly different appearances.
In addition to structural similarities, homology can also describe the shared ancestry of proteins and DNA sequence. High amounts of sequence similarity between two species at a particular gene suggests that the gene is derived from a common ancestor shared between the two species. In certain cases, the gene could be extremely conserved, resulting in almost identical sequence similarity, suggesting that the gene of interest comes from a common ancestor and is essential for basic cellular function and survival.
Geneticists utilize two special terms to identify different causes of sequence similarity:
- Paralogs- sequences in the genome that have similarity due to a duplication event, where the sequences often (but not always) evolve new functions [1]
- Orthologs- sequences in different species that have similarity due to a speciation event, where the sequence often (but not always) retains the same function [1]
Figure 2.
Situation (1) on the left depicts a duplication event, followed by two speciation events in the duplicated lines. The initial duplication event produces two paralogous genes, the red gene and the blue gene. The following speciation events produces twos sets of orthologous genes, 1A-2A and 1B-2B.
Situation (2) depicts the event of situation 1 in reverse. First, a speciation event occurs, followed by a duplication event. In this case, each copy is orthologous to the two copies on the opposite side of the speciation branch.
ERCC6 in Common Organisms
Gorilla gorilla gorilla (Western Lowland Gorilla)
ERCC6, Accession: G3QVF5 1,493 Amino Acids, 99.13% Identity Ailuropoda melanoleuca (Giant Panda)
ERCC6 (isoform 2), Accession: XP_019663426 1,442 Amino Acids, 84.61% Identity Gallus gallus (Red Junglefowl)
ERCC6 (isoform 2), Accession: XP_015143904 1,456 Amino Acids, 64.55% Identity Monodelphis domestica (Gray Short Tailed Opossum)
ERCC6 (isoform 1), Accession: XP_001366076 1,492 Amino Acids, 69.24% Identity |
Pan troglodytes (Common Chimpanzee)
ERCC6 (isoform 2), Accession: XP_009438633 1,454 Amino Acids, 99.46% Identity Loxodonta africana (African Bush Elephant)
ERCC6, Accession: XP_003409139 1,501 Amino Acids, 82.19% Identity Oreochromis niloticus (Nile Tilapia)
ERCC6, Accession: XP_005474178 1,437 Amino Acids, 56.65% Identity |
References
all organism gene data hyperlinked to accession numbers
all identity percent information and protein length information from UniProt, Ensembl, and EntrezGene
[1] Jensen, R. A. 2001. Orthologs and paralogs - we need to get it right. Genome Biology, 2(8), interactions1002.1–interactions1002.3.
Images and Videos
Cover photo: http://www.isciencemag.co.uk/features/the-rise-of-homo-sapiens/
Wing, fin, arm homology picture: http://evolutiontale.com/homology/
Ortholog and Paralog Picture: http://ecoevo.unit.oist.jp/lab/?page_id=791
all organism pictures have hyperlinks
This website was created for Genetics 564 by Zachary Beethem, an undergraduate genetics major at UW-Madison.
He can be reached via email: [email protected]
Date of last website update: April 2017
all organism gene data hyperlinked to accession numbers
all identity percent information and protein length information from UniProt, Ensembl, and EntrezGene
[1] Jensen, R. A. 2001. Orthologs and paralogs - we need to get it right. Genome Biology, 2(8), interactions1002.1–interactions1002.3.
Images and Videos
Cover photo: http://www.isciencemag.co.uk/features/the-rise-of-homo-sapiens/
Wing, fin, arm homology picture: http://evolutiontale.com/homology/
Ortholog and Paralog Picture: http://ecoevo.unit.oist.jp/lab/?page_id=791
all organism pictures have hyperlinks
This website was created for Genetics 564 by Zachary Beethem, an undergraduate genetics major at UW-Madison.
He can be reached via email: [email protected]
Date of last website update: April 2017