The proof that DNA is the genetic material comes from several key experiments:

1. The Griffith's Experiment: This experiment involved two strains of Streptococcus pneumoniae bacteria - the R-type (rough and non-virulent) and the S-type (smooth and virulent). Griffith found that when he killed the S-type bacteria with heat and mixed them with live R-type bacteria, the R-type bacteria transformed into S-type bacteria and became virulent. This suggested that some "transforming principle" from the S-type bacteria was taken up by the R-type bacteria, changing their characteristics. This was later identified as DNA.

2. The Avery-MacLeod-McCarty Experiment: This experiment followed up on Griffith's work. They treated the heat-killed S-type bacteria with enzymes that destroyed proteins, RNA, and other molecules, leaving only DNA. They found that the DNA could still transform R-type bacteria into S-type bacteria, suggesting that DNA was the "transforming principle".

3. The Hershey-Chase Experiment: This experiment used bacteriophages (viruses that infect bacteria). They labeled the DNA of some phages with radioactive phosphorus and the protein of other phages with radioactive sulfur. After allowing the phages to infect bacteria, they found that only the radioactive phosphorus (from the DNA) was found inside the bacteria. This suggested that DNA, not protein, was the genetic material that was passed from the phages to the bacteria.

So, the correct answer to your question is C. Radioactive phosphorous isotope could be detected inside bacteria after an infection with bacteriophages containing this isotope, whereas radioactive sulphur isotope present in other, labelled phages could not.

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The proof that DNA is the genetic material comes from several key experiments:

1. The Griffith's Experiment: This experiment involved two strains of Streptococcus pneumoniae bacteria - the R-type (rough and non-virulent) and the S-type (smooth and virulent). Griffith found that when he killed the S-type bacteria with heat and mixed them with live R-type bacteria, the R-type bacteria transformed into S-type bacteria and became virulent. This suggested that some "transforming principle" from the S-type bacteria was taken up by the R-type bacteria, changing their characteristics. This was later identified as DNA.

2. The Avery-MacLeod-McCarty Experiment: This experiment followed up on Griffith's work. They treated the heat-killed S-type bacteria with enzymes that destroyed proteins, RNA, and other molecules, leaving only DNA. They found that the DNA could still transform R-type bacteria into S-type bacteria, suggesting that DNA was the "transforming principle".

3. The Hershey-Chase Experiment: This experiment used bacteriophages (viruses that infect bacteria). They labeled the DNA of some phages with radioactive phosphorus and the protein of other phages with radioactive sulfur. After allowing the phages to infect bacteria, they found that only the radioactive phosphorus (from the DNA) was found inside the bacteria. This suggested that DNA, not protein, was the genetic material that was passed from the phages to the bacteria.

So, the correct answer to your question is C. Radioactive phosphorous isotope could be detected inside bacteria after an infection with bacteriophages containing this isotope, whereas radioactive sulphur isotope present in other, labelled phages could not.

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The proof that DNA is the genetic material comes from several key experiments:

1. The Griffith's Experiment: This experiment involved two strains of Streptococcus pneumoniae bacteria - the R-type (rough and non-virulent) and the S-type (smooth and virulent). Griffith found that when he killed the S-type bacteria with heat and mixed them with live R-type bacteria, the R-type bacteria transformed into S-type bacteria and became virulent. This suggested that some "transforming principle" from the S-type bacteria was taken up by the R-type bacteria, changing their characteristics. This was later identified as DNA.

2. The Avery-MacLeod-McCarty Experiment: This experiment followed up on Griffith's work. They treated the heat-killed S-type bacteria with enzymes that destroyed proteins, RNA, and other molecules, leaving only DNA. They found that the DNA could still transform R-type bacteria into S-type bacteria, suggesting that DNA was the "transforming principle".

3. The Hershey-Chase Experiment: This experiment used bacteriophages (viruses that infect bacteria). They labeled the DNA of some phages with radioactive phosphorus and the protein of other phages with radioactive sulfur. After allowing the phages to infect bacteria, they found that only the radioactive phosphorus (from the DNA) was found inside the bacteria. This suggested that DNA, not protein, was the genetic material that was passed from the phages to the bacteria.

So, the correct answer to your question is C. Radioactive phosphorous isotope could be detected inside bacteria after an infection with bacteriophages containing this isotope, whereas radioactive sulphur isotope present in other, labelled phages could not.

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