text: Well, simply put, crossing over is what happens when the pair of homologous chromosomes contact each other, their DNA strands (=arms) become attached and some bits of genetic information are exchanged. Then the homologous chromosomes separate; notice that each is slightly different than it was before, because of the new information.\nThis process does not occur in ordinary body cells (otherwise our genetic composition would be variable), but only during the production of gametes (=reproductive cells). After separating, those two "changed" chromosomes that formed a pair in the parental cell will each go to a different gamete.  Thus, instead of having the exact same composition as the parent's cells, some of the gametes will be different. When a gamete combines with another to form a new being, there can always be novel combinations.\nPrecisely one of the advantages of sexual reproduction is the production of variability.\n\nHomologous = matched because each comes from one of the parents (one was in the egg and the other in the spermatozoid) and they have information for the same traits\n\nChromosome =  discrete packages of DNA; they're not visible during most of the cell's life, they only become denser at cell reproduction.\n\nI think the best way to explain this process would be to build a model using kiddie dough with different colors. It doesn't have to be complex, see the illustration at the link.