This biology question covers important biological concepts and processes. The step-by-step explanation below helps you understand the underlying mechanisms and reasoning.
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Step 1: Initial state and replication for 1st generation in N¹⁵ medium. The initial DNA is a Hybrid DNA, meaning it consists of one N¹⁴ strand and one N¹⁵ strand (N¹⁴N¹⁵). When this N¹⁴N¹⁵ DNA replicates in an N¹⁵ medium for the first generation: The N¹⁴ strand serves as a template, and a new N¹⁵ strand is synthesized, forming a N¹⁴N¹⁵ (Hybrid) molecule. The N¹⁵ strand serves as a template, and a new N¹⁵ strand is synthesized, forming a N¹⁵N¹⁵ (Heavy) molecule. After the 1st generation in N¹⁵ medium, we have: 1 Hybrid (N¹⁴N¹⁵) and 1 Heavy (N¹⁵N¹⁵) DNA molecule. Step 2: Replication for 2nd generation in N¹⁵ medium. Now, the 1 Hybrid (N¹⁴N¹⁵) and 1 Heavy (N¹⁵N¹⁵) molecules replicate in the N¹⁵ medium. From the 1 Hybrid (N¹⁴N¹⁵) molecule: N¹⁴ template + new N¹⁵ strand → N¹⁴N¹⁵ (Hybrid) N¹⁵ template + new N¹⁵ strand → N¹⁵N¹⁵ (Heavy) This yields: 1 Hybrid and 1 Heavy molecule. From the 1 Heavy (N¹⁵N¹⁵) molecule: N¹⁵ template + new N¹⁵ strand → N¹⁵N¹⁵ (Heavy) N¹⁵ template + new N¹⁵ strand → N¹⁵N¹⁵ (Heavy) This yields: 2 Heavy molecules. After the 2nd generation in N¹⁵ medium, the total molecules are: Hybrid (N¹⁴N¹⁵): 1 Heavy (N¹⁵N¹⁵): 1 (from original hybrid) + 2 (from original heavy) = 3 Normal (N¹⁴N¹⁴): 0 So, at the end of 2 generations in N¹⁵ medium, we have 1 Hybrid and 3 Heavy DNA molecules. Step 3: Replication for 1st generation in N¹⁴ medium. Now, the 1 Hybrid (N¹⁴N¹⁵) and 3 Heavy (N¹⁵N¹⁵) molecules replicate in an N¹⁴ medium. From the 1 Hybrid (N¹⁴N¹⁵) molecule: N¹⁴ template + new N¹⁴ strand → N¹⁴N¹⁴ (Normal) N¹⁵ template + new N¹⁴ strand → N¹⁴N¹⁵ (Hybrid) This yields: 1 Normal and 1 Hybrid molecule. From the 3 Heavy (N¹⁵N¹⁵) molecules: Each N¹⁵N¹⁵ molecule replicates in N¹⁴ medium. For each N¹⁵N¹⁵: N¹⁵ template + new N¹⁴ strand → N¹⁴N¹⁵ (Hybrid) (twice) So, each N¹⁵N¹⁵ molecule yields 2 Hybrid (N¹⁴N¹⁵) molecules. Since there are 3 Heavy molecules, they will yield 3 × 2 = 6 Hybrid (N¹⁴N¹⁵) molecules. Step 4: Calculate the final ratio. Combining the results from Step 3: Normal (N¹⁴N¹⁴) molecules: 1 Hybrid (N¹⁴N¹⁵) molecules: 1 (from the initial hybrid's replication) + 6 (from the heavy molecules' replication) = 7 Heavy (N¹⁵N¹⁵) molecules: 0 The ratio of Hybrid : Normal : Heavy double-strand DNA is: Hybrid : Normal : Heavy = 7:1:0 3 done, 2 left today. You're making progress.