Insights into non-crossover recombination from long-read sperm sequencing

Meiotic recombination is a fundamental process that generates genetic diversity by creating new combinations of existing alleles. While crossovers in humans are well characterized, the more frequent non-crossovers that lead to gene conversion remain challenging to study. Here we show that single high-fidelity long sequencing reads from sperm can capture both crossovers and non-crossovers, allowing effectively arbitrary sample sizes for analysis from one male. Using fifteen sperm samples from thirteen donors we demonstrate variation between donors for the different types of recombination, even when they share the same PRDM9 genotype. Non-crossovers are less consistent with the genetic map and exhibit reduced association with meiotic double-strand break (DSB) sites identified by DMC1 binding. Where non-crossover gene conversions are close to PRDM9 sites they tend to occur upstream. We further provide evidence for two distinct non-crossover processes. One gives rise to the vast majority of non-crossovers with mean conversion tract length under 50bp, while ~1% of non-crossovers have much longer mean tract length. Applying the same analysis pipeline to public data from twelve blood samples, we also see non-crossover gene conversions, but very few crossover events. These non-meiotic events, not correlated with the genetic map, increase with age, consistent with double-strand break repair throughout life. We suggest that many of the non-crossover events seen in sperm also derive from non-meiotic repair prior to spermatogenesis.

• 14/10/2025
• 1 sample
• DAC: EGAC00001000274
• Technologies: Revio, Sequel IIe