Mitochondrial DNA Copy Number, a Marker of Viability for Oocytes1

Finding a biological marker of viability for oocytes and sperm has been a challenge for reproductive biologists. Such a marker could be used to choose gametes that have a higher chance of producing healthy descendents. This is especially important in humans and would benefit couples facing reproductive problems. The enormous amount of mitochondrial DNA (mtDNA) in oocytes and the fact the mtDNA is not replicated before implantation have led to speculation that the number of mtDNA copies in oocytes could be used as a marker of viability [1–4].