Question

what is cosmid?

Answer 1

A type of artificially created plasmid that has a large capacity for inserted gene fragments, which is to say that you can make it bigger than a normal plasmid construct. It's main difference compared to a normal plasmid construct is that it has so called cos sites which allow them to be packaged into a phages. Thus you can use viruses to transmit the cosmid into your target host cell. This allows the cosmid to be bigger than a normal plasmid since normal plasmids tend to encounter recombination of some sorts after it reaches a certain size, and generally you dont want random recombintion to occur in your meticulously crafted plamid construct.