Final answer:
The usefulness of transgenic organisms depends on the expression of the inserted foreign gene within the host organism, not on the origin of the gene, the type of host, or the vector used.
Step-by-step explanation:
Transgenic organisms can be scientifically or commercially useful only if the inserted ("foreign") gene is expressed in the host organism. Therefore, the correct answer to the given question is option 4.
Genetic engineering involves the addition of foreign DNA to an organism's genome to produce genetically modified organisms (GMOs). When the foreign DNA originates from a different species, the GMO is considered transgenic. For these organisms to be beneficial, the foreign gene must be properly expressed, leading to the production of a desired protein or trait. This expression is crucial regardless of whether the gene is from the human genome, the host organism is a microorganism, or the vector used is a plasmid.
For example, the production of human insulin in bacteria requires the human insulin gene to be not only inserted but also expressed. Hence, the source of the gene, the type of host organism, or the nature of the vector do not solely determine the usefulness of a transgenic organism; it is the successful expression of the foreign gene that is the key factor.