three questions about CRISPR knowout - (Jun/25/2014 )

the first question:

In CRISPR system, CAS9 or CAS9N cut the DNA and DNA could be repaird by non homologous recombination. This may cause the frame shift, and protein translation may be stop when meet the new termination codon.So the protein could be knock out.  But could CRISPR stop the mRNA transcription and why?

the second question:

How could Identify the protein have been knock? Western could work. But can I use PCR to do this work?

the third question

In CRISPR system, the sgRNA have only 20bp, the specificity could not be very good and it may cause other mutation. how could i avoid this problem?

thanks !

Are these homework questions? 

No. they are not homework......