During which stage of meiosis does crossing over occur? Prophase b. Metaphase Anaphase d. Telophase Prophase Il Metaphase g: Anaphase h. Telophase Il Crossing over during melosis
The Correct Answer and Explanation is:
Correct Answer: a. Prophase I
Crossing over takes place during Prophase I of meiosis. This process is a fundamental step in genetic variation. During Prophase I, homologous chromosomes pair up in a process called synapsis, forming structures known as tetrads. Each tetrad consists of two homologous chromosomes, each with two sister chromatids. While in this close alignment, non-sister chromatids may exchange segments of genetic material through a process called recombination or crossing over.
The point where chromatids physically exchange parts is known as the chiasma (plural: chiasmata). This exchange reshuffles genetic information between maternal and paternal chromosomes, increasing the genetic diversity of gametes. The result is that no two gametes are genetically identical, and this variation contributes to the uniqueness of offspring.
Crossing over is tightly regulated and occurs before the chromosomes are separated in the later stages of meiosis. After Prophase I, the cell proceeds through Metaphase I, Anaphase I, and Telophase I, followed by Meiosis II, which resembles mitosis. However, by the time Metaphase I is reached, crossing over has already been completed.
Failure in crossing over or errors during this phase can lead to chromosomal abnormalities or genetic disorders. This highlights the critical nature of Prophase I in ensuring both genetic diversity and chromosomal integrity. Thus, the stage in which crossing over occurs is not just a random moment during meiosis but a highly orchestrated and essential event for sexual reproduction.
