The underlying principle of gene therapy is:
a. replacing a defective copy of a gene with a functional copy
b. silencing a gene so it stops producing mrna
c. making a mutation in an existing gene
d. inserting a promoter to produce large amounts of a protein

Option (A).

Explanation:

Gene therapy may be defined as the type of therapeutic medicine used to treat the genetic problems of the individual. The genetic therapy was first discovered by  Martin Cline.

In the genetic therapy, the defective copy of a gene is replaced by the function copy of gene. The gene can be inserted directly by the injections or by using any retrovirus.

Thus, the correct option is (A).

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

silty loam

hope this