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bioRxiv · 10.1101/2024.12.27.630357

Muller's Ratchet and Gene Duplication

Freund, F.·Wirtz, J.·Zheng, Y.·Schaefer, Y.·Wiehe, T.
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Abstract

Copy number of genes in gene families can be highly variable among individuals and may continue to change across generations. Here, we study a model of duplication-selection interaction, which is related to Haighs mutation-selection model of Mullers ratchet. New gene copies are generated by duplication but fitness of individuals decreases as copy number increases. Our model comes in two flavours: duplicates are copied either from a single template or from any existing copy. A duplication-selection equilibrium exists in both cases for infinite size populations and is given by a shifted Poisson or a negative binomial distribution. Unless counteracted by synergistic epistasis, finite populations suffer from loss of low copy-number haplotypes by drift, forcing them into a regime called run-away evolution in which new copies accumulate without bound nor equilibrium. We discuss a few empirical examples and interpret them in the light of our models. Generally, large gene families appear too over-dispersed to fit the single template model suggesting a dynamic, and potentially accelerating, duplication process.

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Freund, F., Wirtz, J., Zheng, Y., Schaefer, Y., Wiehe, T.. 2024-12-29. Muller's Ratchet and Gene Duplication. https://doi.org/10.1101/2024.12.27.630357

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