 Morpholinos have become a standard knockdown tool in animal embryonic systems , which have a broader range of gene expression than adult cells and can be strongly affected by an off @-@ target interaction . Following initial injections into frog or fish embryos at the single @-@ cell or few @-@ cell stages , Morpholino effects can be measured up to five days later , after most of the processes of organogenesis and differentiation are past , with observed phenotypes consistent with target @-@ gene knockdown . Control oligos with irrelevant sequences usually produce no change in embryonic phenotype , evidence of the Morpholino oligo 's sequence @-@ specificity and lack of non @-@ antisense effects . The dose required for a knockdown can be reduced by coinjection of several Morpholino oligos targeting the same mRNA , which is an effective strategy for reducing or eliminating dose @-@ dependent off @-@ target RNA interactions . 
