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Question:
I've been telling my students about Fred Griffith's experiment and DNA transformation, but when I get to the idea of the rough pneumococcus actually taking the genes from the smooth and thereby transforming itself into a virulent strain, the question always arises in my mind (although usually NOT in my STUDENTS' minds) about the mechanism for this. How exactly did the DNA from the rough obtain those key DNA sequences from the smooth? How did it enter the rough's genome? I imagine that the heat treatment to kill the smooth probably disrupted their capsules, but that still doesn't explain how the rough obtained the DNA from the smooth. Can you help?



Replies:
Are you familiar with transformation experiments in genetic engineering? Many bacteria can take in DNA from the environment, given the right conditions. If the DNA from the smooth were left floating around in the environment after the capsules were disrupted, then at least some of that DNA could be taken into the rough bacteria. Apparently, the "right" segments of gene(s) got in to transform those remaining intact bacteria. Then, they could reproduce, forming lots of virulent "offspring." Does that make sense to you?

Ellen Mayo



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