Male-biased recombination at chromosome ends in a songbird revealed by precisely mapping crossover positions

Recombination plays a crucial role in evolution by generating novel haplotypes and disrupting linkage between genes, thereby enhancing the efficiency of selection. Here, we analyse the genomes of twelve great reed warblers (Acrocephalus arundinaceus) in a three-generation pedigree to identify precise crossover positions along the chromosomes. We located more than 200 crossovers and found that these were highly concentrated towards the telomeric ends of the chromosomes. While the number of recombination events was similar between the sexes, the crossovers were located significantly closer to the ends of paternal compared to maternal chromosomes. The frequency of crossovers was similar between intergenic and genic regions, but within genes, they occurred more frequently in exons than in introns. In conclusion, our study of the great reed warbler revealed substantial variation in crossover frequencies within chromosomes, with a distinct bias towards the sub-telomeric regions, particularly on the paternal side. These findings emphasise the importance of thoroughly screening the entire length of chromosomes to characterise the recombination landscape and uncover potential sex-biases in recombination. Article summaryThe genetic exchange between the paternal and maternal chromosomes during meiosis - recombination - plays a crucial role in evolution by generating new haplotypes that natural selection can act upon. By analysing genomic data of a three-generation family of great reed warblers, we detected precise locations of approximately 200 recombination events in the genome of these birds. This unveiled a prominent sex-bias with recombination occurring more often towards chromosome ends in males than in females.