Law of Independent Assortment
The unit factors that are being referred to in Gregor Mendel's theories are now called genes. In a diploid organism, the genes exist in two alternative forms called alleles. The two forms of alleles are brought together in fertilization. One set of alleles comes from the maternal gamete and the other set from the paternal gamete.
During union of gametes, the alleles are paired together, forming a zygote. The zygote, which bears two sets of alleles from its parents, develops into a new organism capable of reproducing by forming its own gametes. During the formation of its own gametes, the paired alleles would separate and assort independently so that only one member goes into the gamete.