Oocytes were lysed in 5 µl of RLT Plus buffer (Qiagen, Cat. No 1053393) for 10 min at room temperature and bisulfite conversion was carried out directly on the cell lysate to minimise losses using standard manufacture kit (Zymo Research, D5020). DNA was eluted in first strand synthesis mix containing oligos with Illumina adaptor sequence at the 5' end and the random nucleotide sequence at the 3′ end to facilitate binding in all genomic locations Libraries were purified with AMPure XP beads (Beckman Coulter, cat. no. A 63881) and amplified for 13 PCR cycles.