New Evidence Bearing Upon the Problem of the Cytological Basis for Genetical Peculiarities in the Oenotheras

Abstract

Seven species and many hybrids between them were studied cytologically and genetically. The chief cytological results were: (1) Hybrids have characteristic chromosome configurations in diakinesis which they maintain as regularly as do species; (2) these configurations range in the different hybrids from those having a circle of 4 and 5 pairs through various intermediate conditions to those with a circle of 14; (3) reciprocal hybrid combinations have identical chromosome configurations; (4) the % of irregularity in meiosis is not significantly greater in hybrids with large circles than in wild species with corresponding chromosome configurations. Genetical studies showed that hybrids with large circles breed essentially true, as do the species with large circles. Hybrids with smaller circles and more pairs, and therefore with several independent chromosome groups, show splitting progenies, roughly proportional to the number of independent chromosome groups found in the hybrid. The conclusion is that extensive genetical linkage in Oenthera is based upon a linking of the chromosomes. Genes that are linked in species with large circles may be independent in hybrids of these species, when such hybrids show small circles.