Question

the estimated arms effect indicates a 17 - percent increase in yields for herbicide - tolerant cotton adopters nationwide. in some regions, herbicide - tolerant cotton yields may have been lower than for conventional varieties. in particular, farmers in the mississippi portal encountered serious and unexpected problems with their herbicide - tolerant cotton during the 1997 growing season (virginia cooperative extension). some growers found deformed bolls and bolls that dropped off the plants. about 20 percent of the regions herbicide - tolerant cotton was affected. however, the problems may have

Explanation:

For the first question, the passage states that the estimated ARMS effect indicates a 17 - percent increase in yields for herbicide - tolerant cotton adopters nationwide. This is a benefit.
For the second question, the passage mentions that in the Mississippi Portal, some growers found deformed bolls and bolls that dropped off the plants, which means it may have caused problems with the plants.

Answer:

One benefit of genetically modified cotton: It can lead to a 17 - percent increase in yields for herbicide - tolerant cotton adopters nationwide.
One possible drawback of genetically modified cotton: It may have caused problems with the plants.