RNAi knockdown versus DNA knock-out - (Jul/28/2005 )

I'm new in this field and am hoping someone can explain to me why I would want to use RNAi to create knockdown mice over knockout mice.

So far I can understand why short-term RNAi using siRNA is beneficial because the results are fast observed and temporary...? But the process in creating a knockdown mice seems almost the same as when creating a knockout mice. so y bother?

my understanding of the issue is that some genes cannot be knocked-out. or if you do knock out the gene in your mice they become very sickly and will not breed, which makes the long process of creating a knockout not particularly helpful. i haven't used RNAi in mice, so until you commented i figured it would be a lot easier than designing and breeding knockout mice.

Wow, I didn't even know that it was possible to have knock-down mice. I wouldn't really do that anyway because if your silenced protein is crucial for the cells it is likely that you will counterselect them or you may select cells that have found a way to bypass your silenced protein or even more cells mutated for RNAi processing. Am I right? For me looks dangerous even more with off-target effects...