Genetics Experiments

Question 1

Griffith

Answer 1

Transformation in bacteria
(Mice = alive or dead with harmless/virulent/heat killed virulent bacteria)
“Transforming principle”

Question 2

Avery, McLeod & McCarty

Answer 2

Virulent bacteria, heat killed, treated with different enzyme (DNase, RNase, Protease). Added to non-virulent bacteria, cultured, ALL grew except DNase treated.
“DNA is transforming principle”

Question 3

Meselson & Stahl

Answer 3

E. coli in N15 rich environment, (DNA naturally has N14). N15 grown E. coli moved to N14 medium & allowed to reproduce.
Centrifugation = DNA with diff densities.
1st division = N14/N15 50% N14/N14 50%
2nd division = N14/N15 50% N14/N14 50%
“Confirms semiconservative model”

Question 4

Nirenberg & Leder

Answer 4

Very short mRNA with known codon, ribosome & mix of tRNA mixed. Ribosome bound the mRNA & its tRNA. Filtered.
Filter was assayed to see which AA bound.
“To find which codon = which AA”

Question 5

Srb & Horowitz

Answer 5

Looked for biochemical pathway of arginine synthesis etc using neurospora.

Question 6

Beadle & Tatum

Answer 6

Created mutants with xrays where genes encoding AA were damaged. Grown in each of 20 test tubes with different AA.
“Test tube where fungi grew = AA gene which is defective”

Question 7

Hershy & Chase

Answer 7

Bacteriophages used to demonstrate that DNA is genetic material, not protein.
1st exp: Phage produced in radioactively labeled amino acids (using S) so protein was labeled, not DNA.
Phage attacked bacteria, shaking removed the phage from the bacteria but didnt interupt DNA synthesis inside cell.
No radioactivity was located inside bacteria so protein had not been transmitted into cell.
2nd exp: Same thing was done but with radioactively labelled P. After shaking, radioactivity was located inside bacteria, so DNA is genetic material.

Question 8

Watson & Crick

Answer 8

Xray diffraction models & Paired G with C and A with T

Question 9

Chargaff

Answer 9

Ratio of A=T and G=C