Griffith performed early experiments showing that hereditary information could be transferred among bacteria. They took two strains of Streptococcus bacteria: a pathogenic S strain, and a harmless R strain. Mice injected with the harmless R strain lived. Mice injected with the pathogenic S strain died. Griffith then used a heat treatment to kill a sample of S cells, and injected them into mice; this time, the mice lived. Finally, when Griffith mixed heat$-$killed S cells and mixed them with live R cells, the mice died. He concluded that some hereditary factor had been transferred from the dead S cells into the live R cells.

Avery, MacLeod, & McCarty followed up on this experiment to provide early evidence that this hereditary information is carried in DNA. They did so by $...$

Question $22$ options:

sequencing the genomes of the two strains of bacteria and demonstrating that the only difference between them was the presence of a toxin gene.

using microinjection to remove the chromosome from the Streptococcus cells and transfer it into an E$.$ coli cell from which the chromosome had been removed, and then testing whether the recipient cell became more Streptococcus$-$like in its phenotype.

treating the heat$-$killed S bacteria with enzymes that break down nucleic acids before mixing it with the other bacteria; when they did so$,$ the mice lived instead of dying.

growing the bacteria in the presence of $15$N; when they did so$,$ the mice became radioactive, indicating that the isotope had been taken up by the bacteria during reproduction.