is it my recombinant plasmid or contamination? - only two colonies on the plate.... (Dec/30/2005 )
hello again.....i have transformed E coli with my recombinant plasmid by electroporation.....positive control is ok...negative control has no colonies but my samples have two colonies each....E coli strain is not the one that I will use later I used it this time just to if the ligation is ok...so I want to check by pCR directly from the E coli strain...do u think 2 colonies worth checking or its just contamination and my ligation failed?? 
thanx a lot
You should always check the colonies. I have at times got one colony and its been the correct clone. All you need is one...
I agree completely with ML1975 -- I would've written the same answer...
It is always worth checking. I once saw a graduate student get 24 colonies from a transformation. She checked 12 of them for inserts, but all 12 were vector only. She spent another 3 or 4 weeks isolating material to repeat the experiment. I persuaded her to check the other 12 colonies. All of them had the insert.
Having said that, most of the time you need more than twice as many plus insert transformant colonies as no insert control plate colonies in order to reliably find colonies with inserts. So if you have 20 no insert control colonies and 38 colonies on your plus insert ligation colony plate, it will be difficult to find a colony with the insert. Not impossible, but you need to screen everything.
thanx a lot everyone.....ill check the colonies and let you know if ive got the insert....suspense... 
hello everyone!!!!
ok by PCR i could see faint band of my insert!! im so happy...but now imdoing lysis and checking the insert ny RE digestion.....so ill tell you today what happens...
thanx everyone..