A-LevelBiologyNucleic acids and protein synthesis9700/12 · Feb/Mar 2017 · Q261 Mark
Meselson and Stahl investigated DNA in bacteria. They grew bacteria in a medium with only heavy nitrogen, 15N, until all of the bacterial DNA contained only heavy nitrogen. These bacteria were then moved from the heavy nitrogen medium and cultured in a medium with only light nitrogen, 14N. Some bacteria were collected from each of the next three generations and their DNA was analysed. Hybrid DNA contains both heavy and light nitrogen. Which row shows the correct DNA of the first and third generations? [Table 26.1]
Aall hybrid half hybrid, half light
Ball hybrid one quarter hybrid, three quarters light
Chalf hybrid, half heavy one quarter hybrid, three quarters light
Dhalf hybrid, half light one quarter hybrid, three quarters light
✓ Correct answer
B: all hybrid one quarter hybrid, three quarters light
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