Tandem Repeat Evolution Under Selfing and Selection

Why It Matters

Understanding how selfing modulates TR dynamics informs breeding strategies and disease genetics, offering a more accurate framework for predicting genome stability.

Key Takeaways

• Selfing raises homozygosity, boosting recombination variance.
• Stronger purifying selection reduces deleterious TR variants.
• Partial selfing lowers genetic load despite increased drift.
• Stabilising selection under selfing keeps TR lengths optimal.
• Findings guide breeding, conservation, and repeat‑disease research.

Pulse Analysis

Tandem repeats—short DNA motifs that copy themselves in series—have long been recognized as hotspots of mutation and phenotypic variation. Traditional population‑genetic models treat these loci in large, randomly mating groups, implicitly assuming that outcrossing dilutes the effects of recombination and selection. However, many plants, fungi, and some animal species rely on self‑fertilisation, a mating system that drives homozygosity and reshapes the distribution of genetic variation. By foregrounding selfing, researchers can capture a more realistic picture of how repeat length polymorphisms arise and persist in natural populations.

Sudbrack and Mullon combined analytical equations with extensive simulations to track homologous TRs under four selection scenarios: additive purifying, truncation‑like purifying, heterozygote‑penalty, and stabilising selection. Their models reveal that increased homozygosity intensifies the variance generated by unequal recombination within individuals, producing broader TR length spectra. Simultaneously, the same homozygosity sharpens the efficacy of selection, accelerating the removal of deleterious expansions or contractions and consequently lowering the overall genetic load. Even as selfing inflates genetic drift by shrinking effective population size, the amplified selection counterbalances this effect, positioning partially selfing populations in a unique evolutionary niche.

These insights carry practical weight for sectors that manipulate mating systems. In crop improvement programs, controlled selfing could be leveraged to prune harmful repeat expansions while preserving adaptive diversity, enhancing yield stability. Conservation biologists working with endangered self‑compatible species can better anticipate genomic risks associated with inbreeding. Moreover, the link between repeat dynamics and disorders such as Huntington’s disease suggests that inbreeding‑like mechanisms might modulate disease penetrance, opening avenues for novel diagnostics. Future work that integrates empirical TR data with selfing‑aware models promises to refine predictions of genome evolution across the tree of life.