Question

What are some major differences between making transgenic mice by microinjection and creating knockout mice by homologous recombination (before the advent of CRISPR/Cas9 technology)?

Answer 1

Answer:- The key difference is that knock-in is targeted, meaning the desired gene is inserted into a specific locus on the target genome via homologous recombination. For instance,in FFI knock-in in mice, the mutant FFI Prnp gene is located in exactly the locus where Prnp is always located in the mice. This is important because it means the gene will achieve biological (i.e. natural expression) patterns and levels.

By contrast transgenic models use random integration, the desired gene could end up anywhere in the host genome. The desired gene might be placed under its own ( strong) promoter, leading to high levels of expression which can be good for disease models leading to an earlier or robust mode of phenotype. Transgenic organisms generated by pronuclear microinjection typically overexpresses the transgene whereas animals generated by gene targeting are characterized by the deletion or modification of the endogenous target gene.