Traitwell's Future of Genomics Series: Gamete Selection
Who gets stick in the oven and who goes back in the cooler?
We’re continuing our analysis of the future of genomics. For those who are curious, please visit Traitwell.com. Be sure to check out our free apps.
Screening of embryos, brought to term by IVF, is already commercially available. In the simplest case, for the parents of those embryos. Undesirable embryos may be discarded or frozen for future consideration. Gross disorders can be eliminated, or polygenic scores—think sporting ability, intelligence, height and the like, as above—optimized to some extent, given sufficiently many embryos to choose from and declared preferences. As the average age of mothers increases, egg mutations increase dramatically, since the (relatively few) eggs are fixed from the birth of the mother. Aggregation over traits must strengthen modest predictors here, since typically there not that many embryos to choose from (aggregation over instances is weak here). Note though that the IVF procedure is invasive, often painful, and inconvenient, limiting the attractiveness of this procedure to the broader public, quite aside from its unnatural connotations.
There are several directions in which this process will be extended in the near future. There are vastly more sperm–each a random genetic sample from the male—than there will ever be embryos, allowing much more thorough filtering prior to conception. In older males, sperm mutations increase and are almost always harmful where they are functional. With delayed paternity and maternity, increasing numbers of parents will store gametes for future use, then bring them to conception at a more convenient time.
It is not necessary to limit sperm or egg selection to couples, they may be drawn from sperm or egg banks, and then filtered in the same way. Such filtering greatly facilitates the use of germinal repositories to improve reproduction, by sharply raising confidence among users of such services that they will get what they sought. Sperm-shopping for traits will be feasible. Techniques for directed meiosis may also be developed, reducing, where specific results are sought, the role of chance in the recombination brought about by sexual reproduction. (We will deal with gene editing in a more general context, since that is not limited to reproduction.)
As always, similar considerations apply to animals. Consider livestock. Desirable traits are so important to livestock breeding—for example the taste of beef flesh, disease resistance and hardiness–that artificial insemination is prevalent and extensive inbreeding from ‘pure’ lines is rampant. However, elimination of variability by over-application of this process introduces the need to backcross against reservoirs of diversity to provide material for further selection as needs change and new diseases emerge. The use of polygenic scores is already seeing uptake among livestock breeders to accelerate selection for traits and will greatly expand in the future as trait linkage knowledge improves.
Analogous uses exist for pet animals but have been less commonly adopted to date–they will also expand, but one may expect more for behavioural traits than, say, the taste of their flesh.