what is synapsis

Synapsis is the pairing of two homologous chromosomes that occurs during meiosis, allowing for matching-up of homologous pairs prior to their segregation and possible chromosomal crossover between them. It takes place during prophase I of meiosis and is an essential step for a successful meiosis. The crossover of genetic material during synapsis provides a possible defense against chromosome killer mechanisms, by removing the distinction between self and non-self through which such a mechanism could operate. A further consequence of recombinant synapsis is to increase genetic variability within the offspring. In female Drosophila melanogaster fruit flies, meiotic chromosome synapsis occurs in the absence of recombination, and in the nematode Caenorhabditis elegans, meiotic recombination is also unnecessary for homologous chromosome synapsis.