From the Guidelines
Parthenogenesis is a natural form of asexual reproduction where an embryo develops from an unfertilized egg cell, and it can also occur spontaneously in human IVG-derived gametes, which should be reported to a specialized scientific and ethics oversight process 1. This reproductive strategy occurs without fertilization by sperm, resulting in offspring that are genetically identical to the mother (clones) or have slight variations due to genetic recombination during meiosis. Parthenogenesis occurs naturally in certain insects, reptiles, fish, and amphibians, with notable examples including some species of lizards, sharks, and honeybees. In honeybees, unfertilized eggs develop into male drones, while fertilized eggs become female workers or queens. This reproductive method provides evolutionary advantages in environments where finding mates is difficult or when rapid population growth is beneficial. While parthenogenesis has been artificially induced in laboratory settings for some mammals, it does not occur naturally in mammals due to genetic imprinting requirements. The process typically results in offspring that are female, as they inherit X chromosomes from the mother, though some mechanisms can produce male offspring in certain species. Key points to consider:
- Parthenogenetic human embryos are formed without the contribution of human sperm and are subject to category 2 review 1.
- The formation of embryos after fertilization (or parthenogenesis) of IVG-derived gametes requires full review under category 2 1.
- The use of human gametes differentiated from stem cells for the purposes of human reproduction currently falls under a prohibited activity, category 3A, due to unresolved safety issues 1.
From the Research
Definition of Parthenogenesis
- Parthenogenesis is a reproductive strategy where a female gives birth to offspring without a paternal contribution 2
- It is a form of asexual reproduction in which a gamete (ovum or sperm) develops without being fertilized 3
- Parthenogenesis occurs spontaneously in a variety of lower organisms, but not in mammals, although mammalian oocytes can be activated in vitro to undergo parthenogenetic activation 2, 4
Parthenogenesis in Plants
- In plants, parthenogenesis usually occurs in combination with apomeiosis (the omission of meiosis) and pseudogamous or autonomous endosperm formation, together known as apomixis (clonal seed production) 5
- Parthenogenesis in plants can inherit and function independently from apomeiosis and endosperm formation, and can induce embryogenesis in polyploid, diploid, as well as haploid egg cells 5
Parthenogenesis in Animals
- Mammalian oocytes can undergo parthenogenetic activation, but the resultant parthenotes are not capable of developing to term and arrest their growth at different stages, depending on the species 2, 4
- Human parthenogenetic embryos have been proposed as an alternative, less controversial source of embryonic stem cell lines, based on their inherent inability to form a new individual 4
Genetic Aspects of Parthenogenesis
- The inheritance of parthenogenetic embryo development can be studied at the diploid level, and has been shown to be consistent with Mendelian inheritance for a single locus 6
- Genetic characterization of apomeiosis and parthenogenesis has been problematic, but advances have been made in identifying genes involved in parthenogenesis, such as the PsASGR-BabyBoom-Like gene in apomictic Pennisetum 5