Question

At which stage of the cell cycle does crossing over occur?

1) G1 phase
2) S phase
3) G2 phase
4) M phase

Answer 1

Crossing over occurs during prophase of Meiosis I, which follows the interphase stages of the cell cycle but is specifically part of meiosis, not the typical mitotic cell cycle.

Step-by-step explanation:

Crossing over occurs during Meiosis I, specifically in the prophase stage of meiosis. Even though the cell cycle consists of interphase, which includes G1, S, and G2 phases, followed by the M phase encompassing mitosis and cytokinesis, it is important to note that crossing over is not part of the typical cell cycle of mitosis but rather a special event in meiosis. During the S phase of interphase, DNA replication occurs, preparing for cell division.

However, crossing over, which is the exchange of genetic material between homologous chromosomes, occurs later during meiosis, not during the S phase of interphase where only DNA duplication takes place. During prophase I, homologous chromosomes pair up and exchange genetic material through a process called crossing over. This genetic recombination increases genetic diversity and leads to the production of genetically unique offspring.