DNA as the genetic material - L3

Question 1

What was the Sutton-Boveri theory of chromosomal inheritance?

Answer 1

Sutton observed grasshoppers. Boveri observed Ascari worms. They both observed the chromosomes grouping in pairs, and then separating, resulting in gametes that had a reduction in chromosomes.

Question 2

What are S strain and R strain bacteria?

Answer 2

S strain = smooth bacteria, has a polysaccharide coat, is pathogenic, would kill mice.

R strain = rough bacteria, NO polysaccharide coat, NOT pathogenic, would not kill mice so mice lives.

Question 3

What was the Frederick Griffith Transforming principle experiment?
What were the results?

Answer 3

1. Kill S bacteria by heating to high temperatures.
2. Inject dead S bacteria into mice together with live R bacteria.
3. The mice lives
4. Mice die

Inoculation with dead S bacteria + live R bacteria does cause an infection, as mice died. Bacteria from the infected mice do have a polysaccharide coat.

R cells have undergone a “transformation” some sort of hereditary material has passed from the S bacteria to the R bacteria, changing the genotype.

Transforming principle is DNA.

Question 4

What was Hershey and Chases experiment into bacteriophage genetic material?

What were their results?

Answer 4

1. They labelled bacteriophage components DNA 32P or protein 35S with a radioactive isotope.
2. Then let the radioactive phage infect the unlabelled bacteria.
3. Then agitate in a blender to separate phage ghosts/coat from the infected bacteria
4. Centrifuge to separate phage and bacteria based on their weight.
5. Test bacteria and phage for radioactivity with a Geiger counter.

RESULTS?
Most of the radioactivity from protein recovered in phage ghosts outside the bacteria.
Most of the radioactivity from DNA recovered in phage ghosts inside the bacteria.

Therefore, it is the DNA that is being injected and directing the formation of new phage.