History of in heritance notes( Feb, 08)

T.H. Morgan:

• Genes are located on chromosomes, the two constituents of chromosomes - proteins and DNA - were the candidates for the genetic material
• scientists that time tended to believe that proteins were the genetic material

Frederick Griffith:

•  he studied Streptococcus pneumoniae, a bacterium that causes pneumonia in mammals (R and M)
• his experiment: heat-killed S strain were mixed with live R strain bacteria and the mixture were injected into a mouse; the mouse died and the pathogenic stain could be recovered from the mouse's blood.
• Transformation: a change in genotype and phenotype due to the assimilation of a foreign substance by a cell

Further evidence that DNA was the genetic material: viruses infects a host cell and injects its DNA into the host cell to replicate.
Erwin Chargaff:

• four bases of DNA: A, T, G, C
• %A=%T; %G=%C

Watson and Crick:

• discovered the double helix structure of DNA
• their achievement was built on Rosalind Franklin's study ( She used X-ray to find the diffraction pattern of DNA structure.)
• adenine would form two hydrogen bonds only with thymine and guanine would form three hydrogen bonds only with cytosine.