when does crossing over occur and why is it important
Chromosomal crossover
short
pachytene stage of prophase I of meiosis
Chromosomal crossover ( or crossing over ) is the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes during sexual reproduction . It is one of the final phases of genetic recombination , which occurs in the pachytene stage of prophase I of meiosis during a process called synapsis . Synapsis begins before the synaptonemal complex develops and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome .