Copy number is a number of molecules of plasmid that are normally present in single, individual bacterial cell. Plasmids are divided into low copy number and high copy number plasmids on the basis of number of plasmids present in bacterial cell. Low copy number plasmids are usually large in size and present in copy number 1-3 whereas high copy number plasmids are small in size and are present in copy number 10 or more. High copy number plasmids are useful in recombinant DNA technology.
