When does replication occur in mammalian cells?

When does replication occur in mammalian cells?

• A. When the egg and the sperm unite.
• B. During active protein synthesis.
• C. Before the cells divide.
• D. When the cell needs extra energy.

Answer: (C)

Replication happens in preparation for cell division. In mammalian cells this occurs during the S phase of interphase, when the DNA is duplicated so that each chromosome has two sister chromatids. This timing—with replication completed before mitosis begins—ensures that both daughter cells receive a complete set of genetic material. After replication, the cell proceeds through G2 and then divides during mitosis and cytokinesis. It’s not driven by fertilization, nor is it simply tied to ongoing protein synthesis or energy needs.

Replication happens in preparation for cell division. In mammalian cells this occurs during the S phase of interphase, when the DNA is duplicated so that each chromosome has two sister chromatids. This timing—with replication completed before mitosis begins—ensures that both daughter cells receive a complete set of genetic material. After replication, the cell proceeds through G2 and then divides during mitosis and cytokinesis. It’s not driven by fertilization, nor is it simply tied to ongoing protein synthesis or energy needs.