Plasmid is a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA. Plasmids naturally exists in bacterial cells, and they also occur in some eukaryotes. The genes carried in plasmids provide bacteria bacteria with genetic advantages, such as antibiotic resistance. To know whether the cell carry recombinant plasmids; only cells with a plasmid will reproduce and also the color of the colonies in E. coli plasmid recombination experiments allows scientists to distinguish colonies with recombinant plasmids from those without.