Watson and Crick proposed that during DNA replication, the double strand is unwound and each parental strand is used as a template to generate a new daughter strand. The new and old strands then form a new DNA helix. What is this mode of replication called

Semi-conservative.

Explanation:

1. In semi-conservative mode of replication, one strand of parental DNA is serve as a template and it synthesized a new complementary strand to itself and forming a double strand DNA, containing one parental strand and one new strand.

2. In semi-conservative mode of replication, both DNA molecules are same to each other, because both the parental strands serve as template and both synthesize its complementary strand, as G always pairs with C and T pairs with A.