What are plasmids good for?

A plasmid is a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA. Plasmids naturally exist in bacterial cells, and they also occur in some eukaryotes. Often, the genes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance.

Plasmids participate in the transfers of genes in between the populations of bacterias and so participate in the dissemination of genes with selective advantages (such as antibiotics resistance).