what medical problems may result from research into transgenic plants and animals?

Answer 1

Biological expression systems have to be reasonably safe for the research to proceed. The systems employed involve E coli and viruses on a regular basis. I promise you no researcher wants to risk themself or their family becoming infected by their work.

For example to make the human adenovirus safe some of the viruses replication genes are removed so if they were taken out and released they would fail due to an incomplete genome.
However virus stocks could be contaminated by replication competent viruses or even regenerated with stolen host DNA from the propagation cell lines so must always be treated as if they were infective. To handle this potential problem there are biosafety chambers for human infective material and procedures to use so waste material can be destroyed properly even with the incomplete viruses. They are always handled as if hazardous.
Animals expressing human infective material are the greatest risk factor because if they escaped and survived somehow to reproduce in the wild they could create an animal refugium for the human infective virus.
The chances of a manmade vector and gene mutating are exactly the same as a wild type of mutation event in any virus. Many mutations are usually neutral or silent but some are going to shift the function of the protein.

Of course this already happens occasionally with animal viruses when they mutate to infect a new host, us. Transgenic risks happen with viruses in or out of the lab because viruses are inherently capable of becoming DNA vectors between hosts.
There have been many viral infections that have brought new material to humans because we currently use some 16 genes from this viral source. They are called endogenous retroviruses ERV's. Endo-genous means they are now part of the human genome but they were once exo-genous or just regular retroviruses (like the AIDS virus). Some viruses have they ability to become incorporated in the host DNA then re-emerge at a later date. This insertion into the host DNA is called endogenization. If they insert into germ cells they become part of the host species. The vast number of these events that occurred in our ancestores left us with these few 'retrogenes'.
http://www.sciencedaily.com/releases/2005/03/050328174826.htm
Human retrogenes
http://nar.oxfordjournals.org/cgi/content/full/31/15/4385
What happens to the introduced genes over time
http://www.pnas.org/cgi/content/abstract/0511307103v1?etoc

Answer 2

The major concern about transgenetic organisms is the way they are created. Viruses are often used to insert foriegn genes into cells after the viruses themselves are modified to do so. However there exists the possibility of the viral DNA mutating into something which could become very harmful. It would be as catastrophic with plants as it might be with animals. Plant viruses can eliminate the grain supply and this would result in famine. Animal viruses can develop into diseases and cause plagues. Most of the deadliest human viruses are closely related to similar viruses in other animals. AIDS and Ebola have relatives which infect monkeys and rats, but do not kill them. It is believed a chance mutation allowed these animal viruses to be able to live in human cells.

Answer 3

I usually come out with animals with two heads and one leg.