In 1928, a medical official at the Ministry of Health in London, England studied the possibility of creating a vaccine against a type of pneumonia called Streptococcus pneumonia. His name was Frederick Griffith. The disease Frederick was working with was a serious cause of death in this period of time.
Griffith’s experiments contained two strains of a type of bacteria commonly called pneumococci, which mainly caused his killer disease. One of the two strains was deadly to humans and the other was harmless. The only physical difference Griffith could find was that the deadly strain had a smooth-coated surface made of sugar surrounding it, and the harmless strain had a rough-coated surface with nothing protecting it. The reason the sugar-coated strain was so lethal was because the human white blood cells had trouble penetrating the smooth, sugary coat.
When testing his experiments, Griffith used lab mice to prove his theories. First, Griffith injected the smooth-coated strain into the mice. As expected, they all caught pneumonia and died. Then, Griffith tried to kill some of the deadly strain with heat and injected it into the mice. Amazingly, the mice didn’t get pneumonia. Next, he injected the rough-surfaced bacteria into the mice. As expected, nothing happened. Then Griffith injected the killed smooth-coated bacteria along with the harmless bacteria. The mice caught a raging case of pneumonia and died. After this experiment, Griffith performed autopsies on the mice and discovered that the bodies were filled with living smooth-coated bacteria. How could this have happened?
There are two possibilities. Either the dead pneumococci had come back to life, or the harmless strain had transformed into the harmful strain. Griffith found that the rough-coated bacteria had been transformed and had become deadly. Also, the bacteria that had acquired the smooth coat were able to pass it on to future generations. The result was both permanent and heritable.
What caused the alteration? Griffith believed that the harmful strain was unable to produce the smooth coat. Since the substance came from the dead strain, the gene itself was not actually alive. So, the form in the genes must have been transferred by chemical compounds. This occurrence was known as transformation and is now called the transformation factor.Mendel
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