Paralogs

Paralogs are genes that share a common ancestral gene due to a duplication event within the same genome. They arise through various duplication mechanisms, including unequal crossing over during meiosis, retroposition, replication errors, or whole-genome duplications. Paralogs often reside on the same chromosome or different chromosomes and can diverge in sequence and expression over time.

As duplicates accumulate mutations, they may take on new functions (neofunctionalization), partition the original function between duplicates (subfunctionalization), or one copy may become nonfunctional (pseudogenization). Paralogs contribute to genetic novelty and complexity and are central to gene family evolution.

Paralogs are contrasted with orthologs, which are genes in different species that descended from a single gene in the last common ancestor. Correctly distinguishing paralogs from orthologs is important in comparative genomics, phylogenetics, and functional inference. In-paralogs arise after a speciation event within a lineage, while out-paralogs diverged prior to speciation. Duplicates can undergo further duplications, creating families of paralogs such as the globin genes or olfactory receptors. Tandem duplications produce arrays of paralogs near each other; whole-genome duplications yield large-scale paralogous sets.

In research, paralog identification relies on sequence similarity, phylogenetic trees, and synteny information. Paralogs are a major source of functional redundancy and diversification, impacting studies in evolution, development, and disease.