Multigene

Multigene generally refers to a gene that exists in multiple copies within the genome, typically as part of a multigene family composed of related genes. Members of a multigene family share sequence similarity and often function relatedly, but can be expressed in different tissues or developmental stages. Copies can be arranged as tandem repeats (clusters on a chromosome) or dispersed across the genome. Multigene families arise mainly by gene duplication, followed by divergence; mechanisms include unequal crossing over, segmental duplications, and retrotransposition. Duplicated genes may maintain original function (redundancy), partition tasks between duplicates (subfunctionalization), or acquire new functions (neofunctionalization). Pseudogenes may arise when duplicates accumulate disabling mutations.

Functional consequences and regulation: Expression of multigene family members can be coordinated or independently regulated. Regulation may involve shared regulatory elements or distinct promoters. Copy number variation among individuals and populations is common, affecting gene dosage and phenotype in some cases.

Examples: rRNA gene clusters (5S and 18S-5.8S-28S) in tandem repeats, globin gene clusters (α and β), odorant receptor and defensin families, HLA genes in the major histocompatibility complex, cytochrome P450 family.

Importance: Studying multigene families helps understand genome evolution, gene regulation, and adaptation. Technical challenges arise in sequencing and assembling repetitive multigene arrays, and CNVs in these regions are linked to disease susceptibility and drug response.