The key difference between orthologous and paralogous genes is that orthologous genes are the homologous genes found in different species due to speciation, and they perform the same function. In contrast, paralogous genes are the genes found within a single species due to duplication and they can have different functions.
Homology is the process of descending from a common ancestor. Therefore, homologous genes originate from common ancestor genes. Orthologous and paralogous genes are two types of homologous genes. Orthologous genes are found in different species. They have evolved due to speciation, and they may perform a similar function. In contrast, paralogous genes are found within a single species. They are a result of genetic duplication, and they can have different functions.
CONTENTS
1. Overview and Key Difference
2. What are Orthologous Genes
3. What are Paralogous Genes
4. Similarities Between Orthologous and Paralogous Genes
5. Side by Side Comparison – Orthologous vs Paralogous Genes in Tabular Form
6. Summary
What are Orthologous Genes?
Orthologous genes are homologous genes found in different species. They have evolved in different species through speciation. However, the ancestral gene and its function have been preserved through the speciation process. Thus, orthologous genes are found in genomes of different species that share a common ancestor. Moreover, they generally maintain a similar function.
Figure 01: Orthologous Genes
For example, human hemoglobin gene and dog hemoglobin gene are orthologous genes diverged due to speciation. Another example of orthologous genes is the plant Flu regulatory protein present in both Arabidopsis and Chlamydomonas. This gene is also inherited from a common ancestor and evolved in two species due to speciation.
What are Paralogous Genes?
Paralogous genes are homologous genes diverged within a single species. They have evolved due to a mutation that occurred in the genetic duplication process. Therefore, they are present within the same genome. Paralogous genes may carry out different functions. However, studies show that one gene of the paralogous pair generally retains the function of the ancestral gene while the other gene (mutant) of the paralogous pair employs a different function.
For example, human hemoglobin and myoglobin gene are homologous genes that are paralogous. Similarly, the genes encoding for four types of hemoglobins (hemoglobin A, hemoglobin A2, hemoglobin B, and hemoglobin F) are also paralogous genes.
Figure 02: Paralogous Genes
What are the Similarities Between Orthologous and Paralogous Genes?
- Orthologous and paralogous genes are two types of homologous genes descending from a common ancestor.
What is the Difference Between Orthologous and Paralogous Genes?
Orthologous and paralogous genes are homologous genes. Orthologous genes are the homologous genes found in different species due to separation by speciation. Meanwhile, paralogous genes are the homologous genes found within a single species due to duplication. So, this is the key difference between orthologous and paralogous genes. Generally, oorthologous genes carry out the same function as the ancestral gene. In contrast, paralogous genes can have different functions other than the function of the ancestral gene. Therefore, this is another major difference between orthologous and paralogous genes.
Moreover, orthologous genes are present in different species, while paralogous genes are present within a single species. Thus, this too is a difference between orthologous and paralogous genes. The evolution of the orthologous genes takes place due to speciation, while the evolution of the paralogous genes takes place due to duplication.
Summary – Orthologous vs Paralogous Genes
Orthologous and paralogous genes are homologous genes derived from a common ancestor. Orthologous genes are homologous genes present in different species. They become orthologous due to the speciation event. In contrast, paralogous genes are homologous genes present within a single species. They become paralogous due to duplication. Generally, orthologous genes maintain a similar function, while paralogous genes have different functions. So, this is the summary of the difference between orthologous and paralogous genes.
Reference:
1. “Sequence Homology.” Wikipedia, Wikimedia Foundation, 29 Nov. 2019, Available here.
2. “7.13C: Homologs, Orthologs, and Paralogs.” Biology LibreTexts, Libretexts, 25 Sept. 2019, Available here.
Image Courtesy:
1. “Ortholog paralog analog (homologs)” By Thomas Shafee – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Mousehoxgenes” By Bstlee – Own work (Public Domain) via Commons Wikimedia