Q87. The two homologous genes occurring in different species are called
(A) paralogous
(B) orthologous
(C) pseudologous
(D) prologous
The correct answer is (B) orthologous.
Orthologous genes are homologous genes found in different species that evolved from a common ancestral gene through speciation events.
Option Explanations
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(A) Paralogous: These are homologous genes within the same species (or sometimes across species) arising from gene duplication events, often leading to divergent functions like hemoglobin and myoglobin in humans.
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(B) Orthologous: Correct; refers specifically to homologous genes separated by speciation, retaining similar functions across species, such as the FLU regulatory protein in Arabidopsis and Chlamydomonas.
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(C) Pseudologous: Not a standard term in genetics; may confuse with pseudogenes (non-functional gene copies), but lacks recognition in homology classification.
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(D) Prologous: No established use in molecular biology or genetics literature for describing gene relationships.
Homologous genes in different species, known as orthologous genes, form the foundation of comparative genomics and evolutionary biology. These genes diverge after speciation from a shared ancestor, preserving core functions vital for CSIR NET aspirants studying genetics.
Core Concepts
Orthologous genes arise when a single ancestral gene splits across evolving species, unlike paralogous genes from intra-species duplications. This distinction aids functional annotation in biotechnology.
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Speciation separates orthologs, maintaining sequence similarity.
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Duplication creates paralogs, enabling subfunctionalization.
Exam Relevance
In CSIR NET Life Sciences, questions test orthology for evolutionary relationships, as in Q87 identifying orthologous as the term for homologous genes across species.
Practical Applications
Orthologs drive drug discovery by predicting gene functions across species, like human-mouse models in research.
