Gregor Mendel, the "father of genetics" discovered genetic principles for heredity. One is called the Principle of Independent Assortment. In this principle, genes located on the same chromosome assort independently of one another. That is because during meiotic division, particularly during metaphase I, during a process called synapsis, crossing over occurs. Homologous chromosomes form tetrads and exchange genes, resulting in new combinations on the chromosomes. Because these chromosomes were homologous, all that is happening is a rearrangement of similar genes. Thus, when gametes are made, the order and arrangement of genes becomes shuffled. This results in great genetic variation even between siblings.