 Chromosome synapsis

Chromosome synapsis is the close association of homologous chromosomes during meiotic prophase, organized in many organisms by a synaptonemal complex. It aligns homologous partners, each already containing two sister chromatids. Synapsis therefore differs from the attachment between sister chromatids created after DNA replication. ^[ref]

Alignment provides a setting for homologous recombination and the connections supporting later segregation. Pairing, synapsis and a completed crossover are related but distinct events; observing close parallel chromosomes does not alone count exchanges. Their coordination explains how a division can reduce chromosome-set number while maintaining one representative of each homologous set in the products.