(a) While cloning

(a) Bacteriophages.

When we link an alien piece of DNA with bacteriophages or plasmid DNA, we can multiply its numbers equal to the copy number of plasmid or bacteriophage. Biotechnologists always prefer to get a large number of copies of the target DNA. Bacteriophages because of their high number per cell, have very high copy numbers of their genome within the bacterial cell; which can bring the same effect on the linked DNA. Whereas, plasmids support only one or two copies per cell, comparatively less than that produced by bacteriophage. Hence bacteriophage is preferred as a vector over plasmids by biotechnologists.

(b) Rosie is the first transgenic cow, which produces human protein-enriched milk. The milk produced contained human alpha-lactalbumin and was found more nutritionally a balanced product for human babies than natural cow-milk.