• When Streptococcus pneumoniae →pneumococcus) bacteria are grown on a culture plate, some produce smooth shiny colonies →S) while others produce rough colonies →R)
• Mice infected with the S strain →virulent) die from pneumonia infection, but mice infected with the R strain do not develop pneumonia.
• Griffith was able to kill bacteria by heating them.
• He observed that heat-killed S strain bacteria injected into mice did not kill them.
• When he injected a mixture of heat-killed S and live R bacteria the mice died.
• He recovered living S bacteria from the dead mice.
• He concluded that the R strain bacteria had somehow been transformed by the heat-killed S strain bacteria.
• Some ‘transforming principle’, transferred from the heat led S strain, had enabled the R strain to become virulent.
Live virulent S-cells + Live mice → Mice died
Non-virulent R-cells + Live mice → Mice survived
Griffith was able to kill bacteria by heating them.
Heat Killed R-cells + Live mice → Mice survived
Heat killed S-cell + Live R-Cells + Live mice → Mice died
b) Avery, MacLeod and McCarty purified bio chemicals such as proteins, DNA and RNA from the heat-killed S cells, and discovered that it was DNA alone from S bacteria that caused the R bacteria to become transformed.
• In Galapagos Islands from the original seed-eating featured finches many other forms of finches, with altered beaks arose, enabling them to become insectivorous and vegetarian finches.
• This process of evolution of different species in a given geographical area, starting from a point and literally radiating to other areas of geography or habitats is called adaptive radiation.
Rate this question :