X-ray treatment of Oenothera chromosomes

Summary The fertilisation of untreated ovules ofOenothera blandina by pollen subjected to doses of X-rays resulted in F₁ generations consisting of normal plants with no pollen sterility, normal plants with about 50% or more pollen sterility and variant plants usually with 50% or more bad pollen.The pollen-sterile normal plants included seven with segmentally interchanged chromosomes, the remainder examined having only normal chromosomes. Five plants had one ring of four chromosomes, one had one ring of six chromosomes and one had two rings of four chromosomes. The inheritance of the interchanges was traced in several cases. Some of them were not transmitted because they were lethal to pollen carrying them and also failed to form embryo sacs.Most of the variant plants appeared cytologically normal, having seven ring pairs at metaphase 1. Three plants had interchanges, two of them having a chain of four chromosomes as the maximum catenation. The F₂'s of the variant plants consisted of normalblandina with the exception of the narrow leaved one that had a ring of four chromosomes.It is concluded that the variant plants, the pollen sterile normals and the interchange normals in which the interchange was not transmitted through the pollen were all defectives, resulting from deletions produced in the parental pollen by the action of the X-rays.Some indications of a quantitative relationship between X-ray dosage and percentage numbers of variants, pollen steriles and interchange heterozygotes respectively could be traced.