DNA replication is controlled at which of the following checkpoint

DNA replication is controlled at the G1/S checkpoint of the cell cycle. 

The G1/S checkpoint, also known as the Start checkpoint, is a critical regulatory point that determines whether a cell will proceed with DNA replication and cell division. At this checkpoint, the cell assesses its internal and external environment to ensure that conditions are favorable for DNA synthesis and subsequent cell division. Key regulatory proteins, such as cyclins and cyclin-dependent kinases (CDKs), govern the progression through this checkpoint.

Before entering S phase, cells must meet certain criteria, including the availability of sufficient nutrients, growth factors, and energy resources, as well as the absence of DNA damage or replication errors. If conditions are favorable, the cell proceeds from the G1 phase to the S phase, where DNA replication occurs.

If conditions are unfavorable or if DNA damage is detected, the cell may delay progression through the G1/S checkpoint to allow for repair of DNA damage or activation of cellular defense mechanisms. Alternatively, the cell may enter a non-dividing state known as G0 phase or undergo programmed cell death (apoptosis) to prevent the propagation of damaged DNA.

Overall, the G1/S checkpoint serves as a crucial regulatory mechanism to ensure the fidelity of DNA replication and maintain genomic stability during cell division.