Functional diversification, a higher evolutionary rate, and intense positive selection help a limited number of immune genes interact with many continuously evolving pathogens. Repeats in protein-coding regions are a well-known source of rapid functional diversification, adaptive variation, and evolutionary novelty. Repeats play a crucial role in biochemical functions like functional diversification of transcription regulation, protein kinases, cell adhesion, signaling pathways, morphogenesis,

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... NA repair, recombination, and RNA processing. Repeat length variation can change the associated protein's interaction, efficacy, and overall protein network. Repeats have an intrinsic unstable nature and can potentially evolve rapidly and expedite the acquisition of complex phenotypic traits and functions. Because of their ability to generate rapid, adaptive variations over short evolutionary distances, repeats are considered "tuning knobs." Repeat length variation in specific genes, like RUNX2 and ALX4, is associated with morphological and physiological changes across vertebrates. Here we study repeat length variation as a potent source of species-specific immune diversification across several clades of tetrapods. Moreover, we provide a clade-wise comprehensive list of immune genes with repeat types for future studies of morphological/evolutionary changes within species groups. We observe significant repeat length variation of FASLG in Rodentia and C1QC in Primates' contrasting species groups.