How do tetrads form during meiosis?

Tetrads form during meiosis when homologous chromosomes pair up and exchange genetic material in a process called crossing over.

In more detail, the formation of tetrads is a crucial part of the first stage of meiosis, known as prophase I. During this phase, the DNA in the cell's nucleus condenses into visible chromosomes. Each chromosome is duplicated and consists of two identical sister chromatids. Simultaneously, the homologous chromosomes, one from each parent, pair up in a process called synapsis. This pairing forms a structure known as a tetrad, which contains four chromatids.

The formation of tetrads is not a random event but is guided by the synaptonemal complex, a protein structure that temporarily forms between two homologous chromosomes. This complex holds the chromosomes together and facilitates the exchange of genetic material between them, a process known as crossing over or recombination. This exchange of genetic material is a critical aspect of meiosis as it increases genetic diversity among the offspring.

During crossing over, the chromatids of the homologous chromosomes break at the same points and rejoin with the corresponding segments from the other chromatid. This process results in chromosomes that contain a mix of parental genes, rather than being an exact copy of one parent or the other.

After crossing over, the tetrads move to the metaphase plate during metaphase I, where they align in preparation for separation. In anaphase I, the homologous chromosomes separate, but the sister chromatids remain together. This separation reduces the chromosome number by half, a key feature of meiosis.

In summary, the formation of tetrads during meiosis is a complex process that involves the pairing of homologous chromosomes and the exchange of genetic material. This process is crucial for genetic diversity in sexually reproducing organisms.