In recent years, the impact of sperm DNA damage on fertility has become an important issue. The different technologies developed to check sperm DNA fragmentation lead to the same conclusion: DNA damage negatively impacts upon reproductive processes. Oocyte DNA repair capacity is one of the cues to understanding embryo developmental arrest. APEX/Ref-1 (apurinic/apyrimidic endonuclease) is an enzyme involved in the DNA base excision repair pathway removing the abasic sites, the most common DNA decays. In humans, APEX has a multifunctional role, including the control of the redox status of transcription factors. RT-PCR allowed us to detect human APEX transcripts in oocytes, spermatozoa and preimplantation blocked embryos. In parallel, a comparative study on sea squirt Ciona intestinalis (ascidian) indicated that APEX transcripts are clearly detectable in oocytes and embryos until the larva stage, but not in spermatozoa, suggesting the appearance of the paternal contribution to DNA repair during development having arisen only late in Vertebrate evolution. Of additional phylogenetic significance is the observation that sea squirt APEX appears to lack redox transcriptional activity.