How does a tetrad form in prophase I of meiosis?

During prophase I of meiosis, chromosomes condense and pair up with their homologous partners. This pairing is called synapsis. The formation of a tetrad occurs during this process, and it involves the alignment of two homologous chromosomes, each consisting of two sister chromatids. As the homologous chromosomes pair up, they become closely associated along their lengths. This close association allows for the exchange of genetic material between the paired chromosomes, a process known as crossing over.

The tetrad, also called a bivalent, consists of four chromatids arranged in two pairs. The term "tetrad" refers to the four chromatids, while "bivalent" refers to the paired homologous chromosomes. The formation of tetrads facilitates genetic recombination between homologous chromosomes, leading to the generation of genetic diversity among the daughter cells produced by meiosis.