Answer:
Crossing over is the event that occurs during prophase 1 but not during prophase 2.
During crossing over genetic material is exchanged between the non-sister chromatids of homologous chromosomes.
The two homologous chromosomes pair with each other and lie in close proximity during synapsis.
Then the genetic material is exchanged at the points of chiasmata.
It results in the formation of new combinations of alleles which forms the basis for the genetic variation in a population.
