plasmidsand

Plasmids are small, typically circular, double-stranded DNA molecules that replicate independently of the chromosomal genome. They occur widely in bacteria and in some archaea, yeasts, and plants. The term "plasmidsand" is not a standard scientific term; this article uses plasmids to cover the core ideas commonly associated with extra-chromosomal genetic elements.

Most plasmids carry a defined origin of replication and a set of genes that are advantageous but not essential for basic growth. Their size and gene content can vary greatly. Plasmids often exist in multiple copies per cell (high-copy) or in fewer copies (low-copy). They are maintained in populations through selective pressure or specific partitioning systems that ensure that daughter cells inherit plasmids during cell division.

Plasmids contribute to genetic diversity and adaptation by spreading genes through horizontal transfer. They can be transferred between cells by conjugation, a process involving cell-to-cell contact and transfer of plasmid DNA. Plasmids can also be taken up from the environment (transformation) or, in some systems, move via phages (transduction). Many carry accessory genes that confer traits such as antibiotic resistance, metabolic capabilities, or virulence factors, influencing ecological interactions and clinical outcomes.

In biotechnology and research, plasmids are widely used as cloning and expression vectors. Common features include an origin of replication, selectable markers, and a multiple cloning site for inserting foreign DNA. Vector design balances copy number, host range, and stability, while safety and regulatory considerations govern their use in laboratories and clinical contexts.