6Mitosis Mitosis is the process in which a eukaryotic cell separates the chromosomesin its cell nucleus, into two identical sets in twodaughter nuclei.Cell division andcytokinesis
7MeiosisMeiosis is essential for sexual reproduction and therefore occurs in all eukaryotes (including single-celled organisms) that reproduce sexually.
8The Hereditary Material DNAThe HereditaryMaterial
9Discovery of DNA 1869-Friedrich Miescher, Swiss biologist He isolated various phosphate-rich chemicals from white blood cells, which he called nuclein (now nucleic acids)His discoery paved the way for the identification of DNA as the carrier of inheritance.
10The Location of Hereditary Information 1930s- Joachim HammerlingAcetabulariaGreen algaeSingle-celled organism
11Acetabularia Experiment When cap was removed new cap regenerationWhen foot was removed no foot regenerationHammerling’s experiment strongly suggested that the hereditary material is located in the nucleus
12DNA or Protein?Although it was clear that nucleus contains the hereditary information, the exact chemical nature was unknownChromosomes consist of both DNA and proteinsWhich one contains the hereditary information?
13The Transforming Principle 1928-Frederick Griffith, English medical officer started experimenting with Streptococcus pneumoniae to develop a vaccine against pneumonia.he discovered what he called a transforming principle, which is today known to be DNASp bacterium causing pneumonia, exists in two strains
14Griffith’s Experiment The smooth strain (S strain) had a polysaccharide capsule and was virulent when injected, causing pneumonia and killing mice in a day or two.The rough strain (R strain) did not cause pneumonia when injected into mice (it was avirulent), since it lacked a capsule.
16Results of Griffith’s Experiment live R strain was somehow “transformed” into the S strainDiscovery showed that organisms can be genetically “re-programmed” into a slightly different version of themselvesWhen the S bacteria were killed by heat, many substances were released (mixture contains protein, RNA, DNA, lipids, and carbohydratesWhat is the transforming agent?
17What is the transforming agent? 1944-Further experiments done at The Rockefeller Institute in New YorkThree scientists: Oswald Avery, Colin MacLeod, and Maclyn McCarty.First, after heat-killing the S strain of bacteria, the mixture was separated into six test tubesThus, each of the test tubes would contain the unknown “transforming agent”A different enzyme was then added to each tube
18Illustration of the classic experiment demonstrating that DNA is capable of transforming harmless R strain S. pneumoniae into the pathogenic S strain.
19Hershey and ChaseDespite this very clear result, some scientists remained skeptical and continued to think that proteins were likely the genetic molecule.1952-two scientists named Alfred Hershey and Martha Chase performed an entirely different type of genetic experiment to determine which molecule, DNA or protein, acted as the genetic material in phages.