It is for this reason that is referred to as a complementary DNA or cDNA. Though there are numerous processes for synthesizing cDNA, the best way of doing so is by using mature or fully spliced mRNA. This is usually done by using the enzyme reverse transcriptase.
Ammonia is used as refrigerant prominently in the refrigeration systems of food industry like dairies, ice creams plants, frozen food production plants, cold storage warehouses, processors of fish, poultry and meat and number of other applications.
Refrigerant leaks have no odor from Freon. In very high concentrations, dangerous to be in, I understand that there is a faint etherial odor, but you are in serious danger at that point. Dupont sold Freons to America on the grounds that Freons were much safer than the toxic and flammable ammonia then in use.