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

Abstract

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. Apart from this major pattern in the recombination landscape, we found significantly higher frequencies of crossovers in genic compared to intergenic regions, and in exons compared to introns. Moreover, 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. 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.