Plasmid mini made and maxi DNA purification kits can be silica gel or anion exchange, endotoxin free and are used to produce pure plasmids that are small DNA molecules within a cell separated from chromosomal DNA and can replicate independently. They are most commonly found in bacteria as small circular, double-stranded DNA molecules; however, plasmids are sometimes present in archaea and eukaryotic organisms. In nature, plasmids often carry genes that may benefit the survival of the organism, for example antibiotic resistance. While the chromosomes are big and contain all the essential information for living, plasmids usually are very small and contain only additional information. Artificial plasmids are widely used as vectors in molecular cloning, serving to drive the replication of recombinant DNA sequences within host organisms.
Rats are used to make rat monoclonal anti mouse antibodies. There are less rat- than mouse clones however. Rats genes from rodents of the genus Rattus norvegicus are often studied in vivo as a model of human genes in Sprague-Dawley or Wistar rats.