# Substantial non‐homologous recombination and structural variation results from Brassica AABC and CCAB hybrid meiosis

## TL;DR

This study shows that meiosis in certain Brassica hybrids leads to significant genetic shuffling, which could help improve crop breeding.

## Contribution

The study reveals high frequencies of non-homologous recombination and structural variation in AABC and CCAB Brassica hybrids.

## Key findings

- AABC and CCAB hybrids show copy number variation indicative of non-homologous A–C recombination.
- Higher homologous crossover frequencies are observed in centromeric and pericentromic regions.
- These hybrids exhibit increased A–C introgressions that may aid in Brassica breeding.

## Abstract

Meiotic crossovers contribute to genetic diversity and play a crucial role in homologous chromosome segregation. Non‐homologous crossovers in Brassica, involving the exchange of genetic material between genomes, can be valuable for transferring novel traits or characteristics between Brassica species. However, there are a limited number of studies that specifically investigate crossover frequencies in populations of interspecific hybrids. We investigated the distribution and frequency of homologous crossover events, as well as non‐homologous recombination and structural variation, in hybrids between B. juncea (AABB) × B. napus (AACC) (resulting in AABC hybrids; 5 genotypes) and B. napus (AACC) × B. carinata (BBCC) (resulting in CCAB hybrids; 4 genotypes). The analysis was performed on individuals derived from microspore culture of both unreduced and reduced gametes produced by the AABC and CCAB hybrids. All AABC and almost all CCAB unreduced gamete‐derived individuals and most AABC and CCAB reduced gamete‐derived individuals showed copy number variation indicative of non‐homologous (A–C) recombination. Additionally, a higher frequency of homologous crossovers, also in centromeric and pericentromic regions, was observed in the diploid genomes of the AABC and CCAB hybrids. Overall, these hybrid types show high frequencies of A–C introgressions, which may be useful in B. juncea or B. carinata introgression breeding, and this increased recombination frequency may help break up existing linkage disequilibrium blocks in the Brassica A and C genomes.

We show that hybrids between Brassica crop species with different combinations of genomes and chromosomes undergo substantial shuffling of these genomes and chromosomes following meiosis, which may help accelerate breeding progress.