evolutionary genetics · BEGINNER LESSON
Orthologue
An orthologue is a gene in different species that descended from the same ancestral gene through speciation. It is often used as a candidate for comparing gene function across species.
What it is
An orthologue is a gene related to a gene in another species by speciation, the splitting of one lineage into two species lineages. In other words, the two genes came from the same ancestral gene before the species separated. Orthologues are measured and identified by comparing DNA or protein sequence, evolutionary history, and sometimes genome context.
[1] Perspectives on Orthology During the Quest for Orthologs - PMC [2] A Multi-level Perspective on the Evolution of Orthologs and Their Functions - PubMed [3] A comparative approach for selecting orthologous candidate genes in genome-wide association studies across multiple species
How it is used
Because orthologues often keep similar roles, they are useful for transferring gene function information from a well-studied species to a less-studied one. They also support comparisons across species in studies of gene evolution, family history, and traits such as elemental accumulation in plants. However, this use is an inference, not a guarantee.
[1] Perspectives on Orthology During the Quest for Orthologs - PMC [2] A Multi-level Perspective on the Evolution of Orthologs and Their Functions - PubMed [3] A comparative approach for selecting orthologous candidate genes in genome-wide association studies across multiple species
How they are identified and why caution is needed
Orthology inference uses several kinds of evidence, including sequence similarity, phylogenetic analysis, multiple sequence alignment, protein similarity, nucleotide-level conservation, and microsynteny, which is the preserved order of genes in a chromosome region. Some resources also use hierarchical orthologous groups, or HOGs, which organize relationships across deeper evolutionary depths. The sources also stress that orthologues can diverge in biochemical activity and interaction partners, so functional equivalence should be tested rather than assumed. Limits include taxonomically restricted biology, divergence that is not obvious from sequence alone, and benchmarking challenges for some frameworks.
[1] Perspectives on Orthology During the Quest for Orthologs - PMC [2] A Multi-level Perspective on the Evolution of Orthologs and Their Functions - PubMed [3] A comparative approach for selecting orthologous candidate genes in genome-wide association studies across multiple species
SEE THE IDEA
How orthology is inferred and checked
Two genes are traced back to a common ancestral gene before species split.
Sequence similarity, phylogenetic trees, alignment, and genome context are compared.
Biochemical activity and interaction partners are examined before transferring annotations.
Divergence can exist even when genes are orthologues, so the match is a hypothesis.
Shared ancestry plus multiple evidence lines can suggest orthology, but functional similarity must still be tested.
Orthology is an evolutionary relationship; function is inferred separately and may change.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.