Mendel's First Law. Computer artwork of Mendel's First Law, the genetic law of segregation. It was formulated by the Austrian botanist Gregor Johann Mendel (1822-1884), top left, after breeding garden peas (Pisum sp.). Here violet and white flowered parents produce a first generation (F1) with violet flowers. Self-pollinating these gives a 3:1 ratio of violet to white flowers (F2). Each parent has a pair of alleles controlling flower colour. In reproduction, one allele from each parent is randomly picked to help form a daughter plant. The allele for violet flowers is dominant and masks" all the white alleles in F1. However in F2, 1/4 of the plants have two white alleles."