Why are the electrocompetent DH5alpha cells kanamycin resistant but the stocks are not?

I am trying to amplify pGBKT7 vector in DH5alpha E.coli. I made my own stock cell from an old stock in the lab. I did test my stocks for resistance by streaking on normal LB and on LB/Kan plates...

11 November 2018 5,388 3 View