(also called syndesis
) is the pairing of two homologous chromosomes
that occurs during meiosis
. It is a form of chromosomal crossover
. Synapsis takes place during prophase I. When homologous chromosomes synapse, they come closer together until they are connected by a protein complex called the synaptonemal complex
, which contains central and lateral elements. While autosomes
undergo synapsis during meiosis sex chromosomes
usually remain unpaired.
When the non-sister chromatids intertwine, segments of chromatids with the same sequence break apart at and are exchanged in a process known as genetic recombination or "crossing-over". Recombination exchanges genetic material between homologous chromosomes and increases the genetic variability of the offspring. This exchange produces a chiasma, a region that is shaped like an X, where the two chromosomes are physically joined.