Chromosomal crossover (or crossing over) is the process by which two chromosomes pair up an exchange sections of their DNA. This often occurs during prophase 1 of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed until near the end of prophase 1. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome. The result of this process is an exchange of genes, called genetic recombination. Chromosomal crossovers also occur in asexual organisms and in somatic cells, since they are important in some forms of DNA repair.