What is a plasmid?

A plasmid is a small, circular piece of DNA that is distinct from the chromosomal DNA in a cell. It occurs in bacteria and some eukaryotic organisms and can replicate independently of chromosomal DNA. Plasmids often carry genes that confer beneficial traits to the bacteria, such as antibiotic resistance, which can be advantageous for survival in certain environments.

This feature of being extra independent DNA allows plasmids to transfer between bacteria through a process known as horizontal gene transfer, facilitating the spread of these traits even among different species. Thus, the defining characteristic of a plasmid is its independent replication and its significance in genetic mobility and variation within microbial populations.