Historical Basis of Modern Understanding

Free Response

Explain Griffith's transformation experiments. What did he conclude from them?


Live R cells acquired genetic information from the heat-killed S cells that “transformed” the R cells into S cells.

Why were radioactive sulfur and phosphorous used to label bacteriophage in Hershey and Chase's experiments?


Sulfur is an element found in proteins and phosphorus is a component of nucleic acids.

When Chargaff was performing his experiments, the tetranucleotide hypothesis, which stated that DNA was composed of GACT nucleotide repeats, was the most widely accepted view of DNA’s composition. How did Chargaff disprove this hypothesis?


If the tetranucleotide hypothesis were true, then DNA would have to contain equal amounts of all four nucleotides (A=T=G=C). However, Chargaff demonstrated that A=T and G=C, but that the four nucleotides are not present in equal amounts.