Chromosomal crossing over results genetic variation in populations
It involves exchange of genetic material between the maternal and paternal chromosomes, a process called crossing over or genetic recombination It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis (pachytene) in a process called synapsis.
In humans, crossing over occurs about 2 – 3 times per chromosome pair, between non – sister chromatids only. (not between sister chromatids). Furthermore, crossover configurations can occur in any combination and can lead to dramatically different outcomes.
Only two chromatids are involved in any single crossover, and crossing over occurs at different points along the chromosome. Every meiotic process does not involve crossing over in the same set of genes each time, but there is at least one crossover per homologous pair. Still, when crossing over is observed in a meiotic division, up to half of the products of that division result in a recombination of DNA between the homologues. This recombination means the homologues are now different than the parent's chromosomes; therefore, each may carry a different set of genetic information.
This process is a source of genetic recombination and produces recombinant chromosomes. Since crossing–over allows shuffling of genetic material between maternal and paternal homologous chromosomes, it results in genetic recombination. This shuffling ensures genetic variability in a population. That's why individuals look different from one another.