Chromosomal crossover is the natural pairing up and exchanging of genetic material between

The correct answer is:

Homologous chromosomes

• A chromosomal crossover or crossover is the exchange of genetic material during sexual reproduction between non-sister chromatids of two homologous chromosomes, resulting in a recombinant chromosome.
• This is one of the final stages of genetic recombination that occurs during the pachytene stage of prophase I of meiosis during a process called a synapse.
• Synapses begin before the synaptonemal complex develops and are not completed until late in prophase I.
• Crossovers usually occur when a matched region on a matched chromosome breaks and then rejoins the other chromosome increase.