During the 1940s the widely accepted conclusion was that genes were morelikely to be made of protein, DNA merely provides a structural framework in chromosomes, Conclusive experimental evidence that genes are made of DNA came from studies of (a) bacterial transformation and (b) virus replication. 1928 Griffith :!: Bacterial transformation streptococcus pneumoniae: two types S strains-virulent : caused lethal pneumonia in mice, can be isolated from blood of dead mice, bacterium has a polysacharide coat, forms large slimy colonies on an agar plate. R strains does not kill mice, doesn't make a polysacharide coat gows as small rough colonies on agar plates.
Griffith's experiments: inject mice with different strain types observe effect on the mice and analyse their blood for bacteria
Explanation for bacterial transformation: The killed Type IIIS did NOT come back to life. Genetic material contained in type IIIS type cells has leaked out and entered the type IIR type, the genetic material has has converted or transformed cells of the IIR type into IIIS type cells. The genetic material from the type IIIS contains the information for making the polysacharide coat required for virulence an example of horizontal gene transfer.
Horizontal gene transfer is the movement of genetic material between unicellular and/ or multicellular organisms other than by vertical transmission of DNA from parent to offspring(reproduction)
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