Adult testes were dissociated and round spermatids were collected by flow cytometry. Cells were fixed in 1% formaldehyde and sonicated. Libraries were prepared using the Accel-NGS 2S Plus DNA Library Kit (Swift Biosciences #21024) according to the manufacturer’s instructions, except that size selection was performed after (instead of before) PCR amplification. Sequencing was done on an Illumina HiSeq2500 with 40 bp single-end reads, with multiplexing (3 samples per lane). Barcode: TTAGGC.