Crossing over is the process by which genetic information is exchanged between two homologous chromosomes
Independent assortment describes the way in which traits are inherited: i.e. different alleles on different chromosomes are inherited independently of one another (in a simple example, a tall green plant can cross with a yellow small plant to make a tall yellow plant or a small green plant - the two traits aren't inherited together.
Therefore, both of these increase the amount of variety present in the gamete, as they both generate new combinations of alleles to pass on to the next generation.
