E. BAUR concluded that the ' aurea ' phenotypes are heterozygous, the green ones are homozygous and that the ivory seedlings represent the homozygous recessive form. In this case is the lethality easy to explain. The pale appearance is obviously caused by the absence of chlorophyll and as soon as the reservoir of nutriments is used up, is the development stopped, because the plants cannot feed any more. A range of such varieties is a suitable basic material for studies on developmental physiology. A close analysis with modern techniques allowed conclusions concerning the time point and way, in which single genes influence the development.
Lethality is a relative term.
It means that an individual cannot survive under certain environmental conditions, though it may develop normally under altered conditions. Plants without chloroplasts, for example, can survive, if cultured on sugar-containing substrates and with addition of growth factors. He found only dark seeds in the F 1 generation, in the F 2 generation did he obtain 630 dark and 40 light seeds. In the F 2 generation do thereby develop 15 individuals in a dihybrid scheme, in which at least one of the genes is present in a heterozygously dominant condition. All genotypes that contain at least a dominant N or M lead to the development of dark seeds, only a doubly recessive homozygous condition causes light seeds.