Week's Molecular Biology Term:

Fosmid

1. Fosmids are similar to cosmids but utilizes the bacterial F-factor (The Fertility factor or F factor is a bacterial DNA sequence that allows a bacterium to produce a sex pilus necessary for conjugation).
2. Fosmid is capable of containing much larger pieces of DNA, up to 50 kilobase (kb) compared to about 10 kb in a plasmid vector.
3. Unlike plasmid vectors, E.coli can only ever contain one fosmid and therefore yields a much lower copy number when cloning. But low copy number offers higher stability than comparable high copy number cosmids.
4. Fosmid system may be useful for constructing stable libraries from complex genomes.