0In 1868 the scientist Friedrich Miescher at first isolated a phosphorous-containing substance called nuclein from nuclei of leukocytes. Miescher and many others suspected that nuclein or nucleic acid is associated in some way with cell inheritance. But the first direct existence that DNA is the carrier of genetic information came in 1944, which was found by scientists, Oswald T. Avery, Colin Macleod and Maclyn McCarty. These scientists found out that DNA extracted from a virulent, i.e. disease-causing strain of the bacterium streptococcus pnemoniae also pneumococcus genetically transformed a non-virulent strain of this organism into a virulent form. Hence they concluded that the DNA extracted from the virulent strain carried the inheritable genetic message for virulence.
