Final answer:
Frederick Griffith's experiments with Streptococcus pneumoniae demonstrated that a 'transforming principle' from dead pathogenic bacteria could change live nonpathogenic bacteria into a virulent form, leading to the groundbreaking conclusion that DNA is the genetic material responsible for heredity.
Step-by-step explanation:
Frederick Griffith's transformation experiments played a pivotal role in understanding genetic material. He worked with two strains of Streptococcus pneumoniae: a nonpathogenic rough strain (R) and a pathogenic smooth strain (S). By injecting these strains into mice in different combinations, he discovered that the dead S strain could transform the live R strain into a pathogenic form. Griffith concluded that a 'transforming principle' transferred from the heat-killed S strain to the live R strain, altering its hereditary material. This principle laid the groundwork for the discovery that DNA is the genetic material responsible for heredity.
Griffith's critical observations led him to consider that genetic material could be passed horizontally, not only from parent to offspring, but also between organisms of the same generation. His conclusion was that the genetic material from dead bacteria could indeed transform living bacteria. Later, in the 1940s, Avery and his colleagues identified DNA as the 'transforming principle', supporting Griffith's findings and furthering our understanding of the role of DNA in heredity.