Monohybrid cross: a cross, developed by Gregor Mendel, that illustrates Mendel's First Lawplugin-autotooltip__default plugin-autotooltip_bigMendel's First Law: also called Mendel's Law of Segregation. It states that during gamete formation, the two alleles at a gene locus segregate from each toher; each gamete has an equal opportunity of containing either allele.. See Chapter 03.