Final answer:
In Prophase 1 of meiosis, the formation of a tetrad occurs when homologous chromosomes pair up through the synaptonemal complex and chiasmata.
Step-by-step explanation:
In Prophase 1 of meiosis, each chromosome pairs with its corresponding homologous chromosome to form a structure called a tetrad. This pairing, known as synapsis, occurs through the formation of a synaptonemal complex. With four chromatids involved, the structure is aptly termed a tetrad because it consists of four sister chromatids. These chromatids are held together at chiasmata, points where crossing over has occurred, exchanging genetic material between chromosomes, which enhances genetic variation in the resulting gametes.
During this phase, the nuclear envelope disintegrates and prepares the homologous chromosomes for the eventual separation during meiosis II. The process of crossing over and the formation of the tetrads are crucial for the genetic diversity of sexual reproduction. The accurate alignment of genes between the non-sister chromatids supports the exchange of genetic information, increasing the genetic variability in gametes.