The Genetic Architecture of Economically Important Traits Provides Major Challenges for the Implementation of Gene Editing in Livestock

Abstract

Gene editing has been hyped as a game-changer in many biological fields including medicine and agriculture. This includes the promise to manipulate the DNA of livestock animals at sufficient throughput, both in terms of number of loci and animals, to consider gene editing as a routine component of livestock breeding programmes. In this essay I will argue that the application of gene editing for complex traits in livestock will prove extremely challenging for a number of reasons: 1) our understanding of the genetic control of complex traits remains sketchy; 2) even with cutting edge ‘omics technologies, the identification of functional mutations remains very challenging; 3) before selecting certain mutations for gene editing, we need to capture the pleiotropic effects of the mutation and test whether its effects are truly additive. With the current understanding of complex traits there is a risk that gene editing will revert to a candidate gene approach without knowledge or understanding of where the important mutations reside. This means that it will be some time before we can really benefit from gene editing for truly complex traits in livestock. In the meantime gene editing could deliver quick wins by ‘repairing’ lethal recessive defects that are present in many elite breeding animals. Furthermore I will outline how gene editing can have an important role in the identification of QTN via in-vitro genetics.