What is ortholog and paralog?

Published by Charlie Davidson on

What is ortholog and paralog?

Orthologs are genes in different species evolved from a common ancestral gene. Paralogs are gene copies created by a duplication event within the same genome.

What is a protein ortholog?

Orthologs are genes which evolved from a common ancestral gene by speciation that usually have retained a similar function in different species. Paralogs are genes related by duplication within the genome and often they acquire a new function.

What does homolog ortholog and paralog mean?

Orthologous are homologous genes where a gene diverges after a speciation event, but the gene and its main function are conserved. If a gene is duplicated in a species, the resulting duplicated genes are paralogs of each other, even though over time they might become different in sequence composition and function.

What is a human ortholog?

Orthologs are genes in different species that evolved from a common ancestral gene by speciation, and, in general, orthologs retain the same function during the course of evolution. Identification of orthologs is a critical process for reliable prediction of gene function in newly sequenced genomes.

Why do paralogs share sequence similarity?

Paralogs typically have the same or similar function, but sometimes do not. Due to lack of the original selective pressure upon one copy of the duplicated gene, this copy is free to mutate and acquire new functions. Paralogous sequences provide useful insight into the way genomes evolve.

What are protein homologs?

Two proteins are homologous if they have a common ancestor, whatever their sequences, structures, or functions. Homology = common ancestry. Homology may or may not result in Similarity: a single mutation leads to a homologous protein, and yet may drastically change the structure and/or function.

What is an example of an ortholog?

Orthologs are genes related by common descent, i.e., “true” homologs. An example would be the beta-hemoglobin genes of human and chimpanzee. Paralogs are genes related by gene duplication.

What are human orthologs?

How does whole genome duplication occur?

Polyploidy, or whole genome duplication is a product of nondisjunction during meiosis which results in additional copies of the entire genome. Polyploidy is common in plants, but it has also occurred in animals, with two rounds of whole genome duplication (2R event) in the vertebrate lineage leading to humans.

What’s the difference between a paralog and an ortholog?

A2 and B2 are paralogs of each other. A common misconception is that paralogous genes are those homologous genes that are in the same genome while orthologous genes are those that are in different genomes. As you can see in the example above, this is absolutely not true.

Can a paralogous protein be derived from an orthologous protein?

While sets of orthologous and paralogous proteins can be easily derived from complete genomic sequences, our method can identify putative specificity determinants in such proteins.

How are homologs and paralogues related to each other?

1 Homolog or homologue. A gene related to a second gene by descent from a common ancestral DNA sequence. 2 Ortholog or othologue. Orthologs are genes in different species that evolved from a common ancestral gene by speciation. 3 Paralog or paralogue. Paralogs are genes related by duplication within a genome.

How are orthologs and homologs related in DNA?

As with anatomical structures, homology between protein or DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either a speciation event (orthologs) or a duplication event (paralogs).

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