(a) Separating plasmid from bacterial chromosome Purifying cloned DNA Bacterial cells containing plasmids Lyse cells, extract DNA (b)Separating insert from plasmid vector Treat with ethidium bromide →閔閤·閤閤A Cut with EcoRI Separate fragments by size Add to solution of Cscl and centrifuge Cscl forms density gradient DNA settles according to its density. Cloned fragment Vector →8 Host chromosomal DNA