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By the early twentieth century, geneticists had associated the presence of genes with chromosomes. Research began to focus on exactly which chemical component of chromosomes composed the genetic material.
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Cell staining techniques provided the first pieces of evidence that DNA was the genetic material.
Experiments showed that one strain of bacteria could be genetically transformed to another strain and that DNA was the transforming agent.
Experiments using radiolabeled protein and DNA identified DNA as the material injected by a virus during its infection of a host cell.