THE INHERITANCE OF FRUIT SIZE IN THE TOMATO

Abstract

It is pointed out that size data from over 50 tomato crosses are explained by the assumption of the geometric action of size factors but not by a simple additive theory.The fact that the F₁results fitted such a theory was pointed out in a previous paper when the theory was proposed. The analysis is here extended to the F₂generation and to cell size measurements.The use of the geometric scale introduces regularity into the otherwise unpredictable F₂segregations, and they become amenable to a simple logarithmic scheme. Analysis by such a scheme indicates that differences in cell number or ovary size are caused by the segregation of three to five pairs of major genes, whereas mature cell size differences seem to be brought about by the segregation of at least twice as many factors.Final weight is thus the resultant of the proportionate action of the following factors:—1. The number of mitotic divisions in the pre-anthesis period and therefore the number of cells at anthesis.2. The cell expansion after anthesis.3. Fruit shape, locule number, and other size-modifying effects.