In the early 20th century, there was significant debate about what molecules were the hereditary material in living cells. Choose Frederick Griffith's experiments with lethal S and nonlethal R strains of bacteria or Avery, McCarty, and MacLeod's continued experiments with the bacteria and answer the following:

a. Summarize the experimental procedures and findings.

b. Explain how the experimental results supported the idea that DNA is the hereditary molecule in cells.

1. Griffith in his experiment used two related strains of bacteria (Streptococcus pneumonia), known as R and S and mice, trying to develop a vaccine against pneumonia. R strain-formed nonvirulent, rough-edged colonies

S strain - rounded and smooth colonies, with sugar protection coat, virulent

Mice that were injected with S strain developed pneumonia and died.

But, when mice were injected with heat-killed S strain it did not cause disease in mice.

The next part of experiment is the injection of combined harmless R bacteria with harmless heat-killed S bacteria. The result was that the mouse developed pnenumonia and in blood sample from the dead mouse, living S bacteria were found.

2. From his experiment, Griffith concluded that injected together, R strain and S strain bacteria most likely "communicate". The R-strain bacteria took "transforming principle" (we know today that this is genetic material DNA) from the heat-killed S bacteria which allowed them to "transform" into virulent bacteria.