At what stage in meiosis does the event “crossing over” occur? Group of answer choices Telophase I Anaphase II Metaphase II Prophase I
The Correct Answer and Explanation is:
Correct Answer: Prophase I
Explanation:
The event known as crossing over occurs during Prophase I of meiosis. This stage is critical in ensuring genetic diversity among sexually reproducing organisms. During Prophase I, homologous chromosomes—pairs of chromosomes containing the same types of genes, one inherited from each parent—come together in a process called synapsis. Once paired, these homologs form structures known as tetrads, consisting of four chromatids.
At this point, sections of chromatids from homologous chromosomes may break and exchange segments in a process known as genetic recombination or crossing over. The physical sites where these exchanges take place are called chiasmata (singular: chiasma). Enzymes facilitate this precise exchange, ensuring that the genetic material is not lost or duplicated.
This recombination results in new combinations of alleles on each chromosome, increasing genetic variation in the resulting gametes. Genetic diversity is vital for evolution and adaptation, giving populations the ability to survive changing environments.
In contrast:
- Telophase I marks the end of the first meiotic division, when homologous chromosomes reach opposite poles and the cell begins to split.
- Anaphase II is part of the second meiotic division, where sister chromatids are pulled apart.
- Metaphase II involves chromosomes aligning at the center of the cell before being separated, but no genetic recombination occurs here.
Therefore, the only stage where crossing over is initiated and completed is Prophase I, making it a key contributor to the genetic uniqueness of individuals produced through sexual reproduction.
