August 30, 2013
Avery, McCarty, and MacLeod were giants in the field of genetics
research. In the 1940s, they tried to explain a strange phenomena: When
they killed lethal (deadly) strep bacteria and mixed them with nonlethal
strep bacteria, the nonlethal strain became deadly. And this now-deadly
strain had offspring that were all lethal as well. What substance changed
the nonlethal bacteria into lethal bacteria?
Avery, McCarty, and MacLeod carried out the following experiment: They
heat-killed a sample of lethal bacteria, then divided it into 2 parts. In one
of the parts, they destroyed all the protein. In the other, they destroyed all
the DNA. Then they mixed each part with nonlethal bacteria and injected
the samples into mice. The mice injected with the protein-free sample died.
The mice injected with the DNA-free sample lived
1. What question were they testing?
2. What was the independent variable?
3. What was the dependent variable?
4. What variables did they need to control in the experiment?
5. What could they infer/conclude from their result?
(en.wikipedia.org)
key: ! = nonlethal bacteria
n=bacteria
★= killed lethal bacteria without DNA
u = killed lethal bacteria without protein
