> anti-biotic 'marker genes' ...

> bees who brought pollen back to the 
> hives... 
>... and soon the antibiotics used 
> to treat colonies for disease no 
> longer worked.

The good news is that things have changed significantly since CRISPR came along - the "marker" genes were "exogenous DNA".  Marker genes can, in some cases (like in human disease research) disrupt the function of the cell. CRISPR uses sharper tools now - things  like "Ribonucleoprotein (RNP) complexes".

But the person who linked beehive antibiotic resistance to "makers" in a GMO crop was flatly wrong even at the time, likely due to a misunderstanding of the nuts and bolts of the process.  

First, the "antibiotic marker" is a marker for a lab tech to verify the successful initial genetic manipulation at the cell level, not a "marker" for patent infringement enforcement.  

Second, the antibiotic resistance is invariably resistance to an antibiotic to which very wide resistance already exists, such as ampicillin.  

Third, the use of markers in a petri dish in the lab does not mean that those markers survive intact through cloning, and all the post-selection propagation of the plants that grow the seeds that are sold to the farmer.  While small fragments of an antibiotic-resistance gene may survive in the environment, the barriers to transfer, incorporation, and transmission of antibiotic resistance to anything else (bees, cows, people) are very very high.  Better to focus on instilling some backbone in doctors who "give in" and prescribe antibiotics to satisfy a pushy patient with a viral infection, if you are worried about the spread of antibiotic resistance. 

There have been several studies done on the specific "risk" of spreading antibiotic resistance from such GMOs, and while all have concluded "miniscule risk", my own personal question still remains unanswered -  "Wait a second - if the marker gene does not 'survive in the environment', then how does the 'payload' gene bestowing the introduced trait 'survive in the environment'?"  I don’t have an answer.  Sorry, I dozed through most of biochem, got a "B", never looked back.  I assume that digestion, no matter what is doing the digestion, tends to break things down, so pass the soy sauce, please.

Below are the nuts and bolts of the "marker DNA" as used circa 2005, in a nutshell:

When introducing recombinant DNA into host cells, there is no way to identify which specific cells have been modified and which have not, as the process is very "shotgun" in nature.  So, you have to culture and "screen" the host (most often bacteria) cells.

Using the "positive marker" of antibiotic resistance to ampicillin allows only the modified bacteria to grown in petri dish with agar spiked with ampicillin.  The unmodified bacteria do not grow, making it easy to assure that you are using the modified bacteria in all the tedious molecular cloning work to come.   

There is also "Color expression" (blue/white screening), where the marker produces a visible difference in the cells grown on normal agar.   Processes using color expression would introduce no antibiotic resistance at all, but there's a lot of twitchy factors and technical details that dictate choices in this area.





 

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