Expression cassettes

[PuelloDiablo]

Hey guys,

 

Have a question: when making transgenic animals, you use an resistance cassette for screening the cells(e.g. Neo = G418 resistance), you make chimeras and mate them with wt.

I'm trying to understand an article I'm reading, where they remove the cassette by crossing the F1 generation with mice that has a special recombinase that will excise the cassette.

 

Why do you even need to remove resistance cassettes? Would it matter if you just kept it in the germ line?

[Bluenoise]

I suspect it depends on what they're trying to accomplish.