Final answer:
The binding of ORC and Cdc6 initiates the origin of replication, a critical step in DNA replication to maintain the quality of DNA.
Step-by-step explanation:
When ORC (Origin Recognition Complex) and Cdc6 bind together, it leads to the initiation of origin of replication. This is a crucial step in the process of DNA replication in eukaryotic cells. The ORC first binds to the replication origin, forming a pre-replicative complex, and the Cdc6 joins this complex, assisting in the recruitment of additional proteins that are necessary to start DNA synthesis. This step ensures that the entire genome will be accurately and completely duplicated once per cell cycle, maintaining the quality of DNA. The answer to the student's question is (a) Origin of replication initiation.