Forward genetics a bare minimum for the appearance of specific phenotypes. However, such initial screens were either incomplete as they were missing redundant loci and epigenetic effects, and such screens were difficult to undertake for certain phenotypes that lack directly measurable phenotypes. Additionally a classical genetics approach takes significantly longer. Gregor Mendel experimented with pea plant phenotypes and published his conclusions about genes and inheritance in 1865. Around the early 1900s Thomas Hunt Morgan was mutating Drosophila using radium and attempting to find heritable mutations Alfred Sturtevant later began mapping genes of Drosophila with mutations they had been following. In the 1990s
Johann Karl Nestler stock animals and their offspring Nestler hoped to explain the (genetic history). Examination of the records of the ancestors of the best breeding animals, called by Nestler "developmental history" () was for him the reverse side of the same coin. According to Wood and Orel the search for rules of heredity in sheep created an atmosphere of enquiry about heredity in general, which had influence on later work of Gregor Johann Mendel, himself a student at the Faculty of Philosophy in 1840–43. Nestler was also a very active member of the "Moravian-Silesian Society for Advancement of Agriculture" (, in which