Final answer:
The heat-stable DNA polymerase made polymerase chain reaction (PCR) practical and widely used in modern molecular genetics.
Step-by-step explanation:
The technique that made the heat-stable DNA polymerase practical and led to its widespread use in modern molecular genetics is the polymerase chain reaction (PCR). PCR is an in vitro laboratory technique that amplifies a specific DNA sequence, and it relies on the use of heat-stable DNA polymerase enzymes derived from thermophilic bacteria. One commonly used heat-stable DNA polymerase in PCR is Taq DNA polymerase, which is derived from the thermophilic bacterium Thermus aquaticus. Taq polymerase is able to withstand the high temperatures used in PCR, making it an essential component of the technique.