Different classes of allele vary in terms of the ease by which they can be generated, largely due to the bias of repair pathways towards NHEJ, and the resulting indel mutations. Gene knockouts are perhaps the simplest to produce, since such indel mutations can be used to introduce frameshifts into protein coding sequence (Fig. 4b), making the efficiency of mutagenesis very high. It is important to carefully consider the gene structure when designing such a strategy, since alternative promoters, alternative splicing and alternative polyadenylation signals are all critical factors to consider.
