1. Lesson aims We are going to learn the key features of a genetic organiser (like DNA). We will look at evidence that DNA is the organiser. We will investigate the way that the organiser works. What is your definition of living? Why do living things need a genetic material?

2. Lesson aims We are going to learn the key features of a genetic organiser (like DNA). We will look at evidence that DNA is the organiser. We will investigate the way that the organiser works. What features must genetic material have? Here are some clues! What should it be made of? How will it get from individual to individual and from cell to cell? What must it organise? How will it improve? How will it cope with change?

3. The nature of the genetic organiser It is made of biomolecules. It can be copied easily and mistakes are rare. It has a direct connection with the production of proteins. Its instructions can be of variable length. It must be compact enough to fit inside cells. Lesson aims We are going to learn the key features of a genetic organiser (like DNA). We will look at evidence that DNA is the organiser. We will investigate the way that the organiser works. It must be stable but have enough instability for changes to happen. Its code must have more capacity than is needed. It must be universal.

4. Observation of everyday things gave rise to the idea of spontaneous generation. Muddy soil giving rise to frogs and the action of rain on grain to mice and rats.

5. The Greeks suggested the idea of pangenesis. Pangenes are formed in every organ. They move through the blood to the genitals and then to the children. This idea results in many of the links between blood and heredity.

6. Soon after the invention of the light microscope in the 1700s, it was noticed that the chromosomes of actively growing cells undergo marked changes.

7. In 1869 - Friedrich Miescher discovered a new acidic, phosphorus containing material in the pus on hospital blankets. He later extracted the material from salmon sperm cells. He called this new substance Nuclein.

8. In 1887 Edouard van Beneden reported that the number of chromosomes was a constant for each species In 1902, Walter Sutton observed that chromosomes obey Mendel's rules of inheritance. The nucleus is rich in nuclein.

9. In the 1920s, experiments on bacteria by Fred Griffith showed that material from an organism can transform other individuals of the organism.

10. In the 1930s, Joachim Hammerling discovered that he could alter the characteristics of two varieties of an alga by transplantation experiments. The transplanted algae always reverted to the characteristics of the part containing the nucleus – in the base of the organism.

11. In 1944, Avery, MacLeod and McCarthy extracted the transforming material discovered by Griffith and investigated the effect of treating it with different enzymes. Protease, lipase and RNAase had no effect on the transforming effect of the material. The transforming material precipitated with alcohol – a chemical feature of DNA.

12. In 1952, Briggs and King showed that the transfer of a nucleus into an egg cell could direct its development.

13. In 1952 Hershey and Chase labelled the DNA and protein coats of a type of virus that uses bacteria to reproduce. They allowed the viruses to infect the bacteria but then separated the virus coats from the bacteria.

14. In 1953, Watson and Crick suggested a structure for DNA that suggested a mechanism for copying and coding of information.