Table 1.

Genetic modification techniques used

	Pronuclear Injection	CRISPR/Cas9 Fertilized Eggs PI/EP	CRISPR/Cas9 Embryonic Stem (ES) Cells	Embryonic Stem (ES) cells	Breeding genetically altered mice
Use	To study the effect/function or expression pattern of the transgene	Knockout to study the function of endogenous genes Knockin for targeted transgenesis	Knockout to study the function of endogenous genes Knockin for targeted transgenesis	Knockout to study the function of endogenous genes Knockin for targeted transgenesis	To generate multigenic disease models
Method of introduction	Pronuclear Injection of fertilized egg	Cytoplasmic Injection, Pronuclear Injection or Electroporation of CRISPR/Cas9 + oligo DNA or targeting vector	Electroporation of CRISPR/Cas9 + oligo DNA or targeting vector	Electroporation of complex targeting vector and selection of homologous recombinant	Cross breeding
Resulting Modification	Random integration of Transgene	Indel, point mutations, integration of complex allele	Indel, point mutations, integration of complex allele	Indel, point mutations, integration of complex allele	Dependent on parental strains
Gene expression	Dependent on regulatory sequence, copy number, integration site of the Transgene	Dependent of endogenous gene regulation Efficient and stable gene expression in safe habor loci	Dependent of endogenous gene regulation Efficient and stable gene expression in safe habor loci	Dependent of endogenous gene regulation Efficient and stable gene expression in safe habor loci	Dependent on parental strains
Timeline From procedure execution to Fo birth	2–3 months	6 months	Multiple steps/1–2 years	1–2 years	2–3 years to crossbreed multiple strains
Notes	Need to select a stable line from multiple founder lines	Founders are likely to be mosaic. Need to confirm germ-line transmission *EP = electroporation	Need germ-cell competent ES cells, chimera formation and confirm germ-line transmission	Need germ-cell competent ES cells, chimera formation and confirm germ-line transmission	Genetic background depends on parental strains