OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What key process occurs during stage 2 of meiosis?

1. Chromosome replication

2. Chromosome pairs cross over

3. Cell division

4. Chromosome alignment

The correct answer is: Chromosome pairs cross over

During stage 2 of meiosis, which is referred to as meiosis II, the primary process that takes place is the separation of sister chromatids. This stage is characterized by the division of the cells that were formed after meiosis I. In meiosis I, chromosome pairs undergo crossing over, where sections of DNA are exchanged between homologous chromosomes. However, this option focuses on stage 2 specifically, where the key process is the alignment of chromosomes at the equatorial plane of the cell followed by separation into individual chromatids. While crossing over (the exchange of genetic material between homologous pairs) occurs in meiosis I and not in meiosis II, chromosome alignment and subsequent division in meiosis II are crucial for ensuring each daughter cell receives the correct number of chromosomes. After alignment, the sister chromatids are pulled apart, leading to the formation of four haploid cells that will ultimately develop into gametes. Thus, the presence of crossing over as the focus in the second stage is misunderstood; rather, the emphasis should be on the alignment and consequent division of chromosomes.