Paralogous

Paralogous refers to genes that are related by duplication within a genome. When a gene is duplicated, the resulting copies, called paralogs, may retain similar sequences and structures but can accumulate mutations that lead to differences in expression, regulation, or function. Paralogous genes arise through various duplication mechanisms, including unequal crossing over during meiosis, DNA replication errors, retrotransposition, and whole-genome duplications.

Paralogous genes are distinct from orthologous genes, which are related by speciation events and reside in different species. Distinguishing paralogs from orthologs is important for comparative genomics and functional inference, as paralogs within a genome can diverge in function, while orthologs across species often retain the same role. Phylogenetic analyses and assessments of synteny are commonly used to classify gene relationships.

Evolutionary outcomes of gene duplication include neofunctionalization, where one copy acquires a new function; subfunctionalization, where the original function is partitioned between duplicates; and nonfunctionalization, where one copy becomes a pseudogene. Duplicates can also be retained due to dosage balance or because both copies provide selective advantages in different tissues or developmental contexts. Over time, paralogous gene families can expand or contract, contributing to phenotypic complexity and lineage-specific traits.

Examples of paralogous gene families include the globin genes (such as alpha-, beta-, and myoglobin), the Hox gene clusters that underpin body-plan organization, and various receptor families that diversify in ligand recognition. Identifying paralogs relies on sequence similarity, phylogenetic relationships, and conserved genomic context.