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.
Crab meat is highly perishable. If it has any hint of an ammonia odor, then its definitely no good. Cooked or canned crab meat should be kept refrigerated until its actually used. Sitting out for hours is bad news.