The number of copies of a particular sequence of DNA, a particular gene, or a particular set of genes, in the haploid genome of an organism.The number of plasmids per bacterium. Plasmids which are replicated easily and often are called "high-copy-number plasmids"; plasmids which are more strictly controlled in their replication are called "low-copy-number plasmids." The different types have different uses to a geneticist.