A few eggs are extracted from a woman and fertilized; each resulting sibling embryo is biopsied for a few cells which are sequenced. A single polygenic score is used to rank the embryos by predicted future trait-value, and surviving embryos are implanted one by one until a healthy live birth happens or there are no more embryos. By starting with the top-ranked embryo, an average gain is realized.
The basic form of this technology, involving simple genetic testing for karyotype (chromosome numbers) and specific (near)-monogenic diseases (e.g. Tay-Sachs) has been used in humans for years. However, the most recent iteration that involves scoring embryos for polygenic traits (e.g. height, intelligence, type 2 diabetes) has only been used a few times so far.
There is another upcoming technology in this area: iterated embryos selection. Here we select on embryos while also applying in vitro gametogenesis to generate gametes (eggs and spermatozoa) from embryos, thus skipping the step of having to birth a human:
(Also called “whizzogenetics”, “in vitro eugenics”, or “in vitro breeding”/IVB.) A large set of cells, perhaps from a diverse set of donors, is regressed to stem cells, turned into both sperm/egg cells, fertilizing each other, and then the top-ranked embryos are selected, yielding a moderate gain; those embryos are not implanted but regressed back to stem cells, and the cycle repeats. Each “generation” the increases accumulate; after perhaps a dozen generations, the trait-values have increased many SDs, and the final embryos are then implanted.
This approach is nearing reality, as various academic publications note, e.g. "Artificially produced gametes in mice, humans and other species" (2021), "Overview of In Vitro Gametogenesis in Mice, Future Applications, and Related Social Changes and Ethics" (2020), "Roadmap of germline development and in vitro gametogenesis from pluripotent stem cells" (2019). There are other uses than genetic selection, since this method allows people to self-fertilize (generate both gametes from one person), and fertilize using homosexual parents (one supplies each gamete type). Bioethicists are already discussing such matters, e.g. "Drawing the line on in vitro gametogenesis" (2020). Thus, to better forecast the potential of human iterated embryo selection, we care about when the component technology will be ready for use.
When will we see the first viable human case of in vitro gametogenesis?
- A trustworthy report of a case of human in vitro gametogenesis leading to a live birth.