In the semi-conservative method of DNA replication, each of the strands of the double helix acts as a template for replication.
Explanation:
Semi-conservative DNA Replication:
Semi-conservative DNA replication produces two daughter helices from the original parent helix. One strand of the daughter helix is form the original template while the other is newly synthesized.
This means that one strand will have the base sequence identical to the parent, while the other will be complementary to the template.
This model was experimentally confirmed by an experiment conducted in 1958 by Meselson and Stahl. They used radioactive isotope of nitrogen i.e. N-14 or N-15. DNA molecules made with N-15 were allowed to replicate in the presence of N-14.
After first replication, DNA molecules contained both N-15 and N-14 isotopes, disproving the conservative model that stated that the new helices are completely identical to the template.
The second replication yielded only N-14 which disproved the dispersive model that the new helices are a combination of both the template and new strands.
* The attached image compares the three proposed models for DNA replication.