During which phase of meiosis do tetrads form?

Tetrads form during Prophase I of meiosis. This phase is significant because it is where homologous chromosomes pair up closely in a process known as synapsis, leading to the formation of a tetrad, which consists of four chromatids—two from each homolog. This pairing is crucial for the process of genetic recombination or crossing over, where segments of chromatids can exchange genetic material, increasing genetic variation in the resulting gametes.

During this phase, various events take place, including the replication of chromosomes and the breakdown of the nuclear envelope. The physical connection between homologous chromosomes allows for the exchange of genetic information, which is essential for the diversity of offspring.

In contrast, the other phases do not involve the formation of tetrads. During Metaphase I, for example, the tetrads align at the cell's equatorial plane, but they are already formed prior to this alignment. Anaphase I involves the separation of the homologous chromosomes, which means the tetrads are splitting, not forming. Finally, Telophase I marks the conclusion of the first meiotic division, where the cell begins to divide into two daughter cells, but by this point, the tetrads have already disassembled.