Final answer:
DNA replication before mitosis is crucial to provide each daughter cell with a complete set of DNA, maintaining the genetic integrity of the organism. This process occurs during the S phase of the cell cycle, resulting in identical copies of chromosomes for distribution to each new cell. The correct option is D.
Step-by-step explanation:
DNA replication must occur before mitosis to ensure that each daughter cell receives a complete set of DNA. During the S phase of the cell cycle, DNA replication produces two identical copies of chromosomes; thus, when the cell divides, each daughter cell inherits a complete set of genetic information.
This replication is essential so that each new cell can maintain its functions and preserve the genetic integrity of the organism. Without DNA replication, or if it were incomplete, the resulting cells would have an incomplete set of chromosomes, leading to loss of genetic material and potentially harmful mutations.
It is critical to note that DNA replication does not create haploid cells or increase genetic variability; those are outcomes associated with meiosis, not mitosis. DNA replication is strictly to ensure that the genetic material is faithfully transmitted to each daughter cell during cell division.