Synapsis occurs during the prophase I phase of meiosis. This is the stage where homologous chromosomes pair up and form a structure known as a tetrad or bivalent. The process of synapsis is crucial because it allows for the exchange of genetic material between homologous chromosomes, a process called crossing over. This genetic recombination increases genetic diversity in the resulting gametes.
During prophase I, the chromosomes condense and become visible under a microscope. The homologous chromosomes then align closely together, and the synaptonemal complex forms between them, facilitating synapsis. This complex helps to stabilize the pairing and ensures that the crossing over occurs accurately.
After synapsis and crossing over, the homologous chromosomes are held together at points called chiasmata. These connections are important for the proper segregation of chromosomes during the subsequent phases of meiosis. Without synapsis and crossing over, the genetic diversity of the offspring would be significantly reduced, and errors in chromosome segregation could lead to genetic disorders.