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OCR A a level biology help

Which of the following statements is/are evidence that DNA replication is semiconservative?
1 After one replication, the number of adenine nucleotides is equal to the number of guanine
2 After two replications, two DNA molecules have one original and one new strand, and two
DNA molecules have two new strands.
3 After three replications, there are eight DNA molecules, only two of which have strands from
the original DNA.

2 and 3 is the correct answer but im confused as to why that is
Reply 1
1) Isn't relevant.
2) If DNA replication wasn't semiconservative, and when it replicated it kept the old strand intact and formed a completely new strand, then there would be only one DNA molecule with original DNA, so the replication must therefore be semiconservative.
3) Is the same logic as 2.

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