THE MAINTENANCE OF SUPERNUMERARY CHROMOSOMES IN WILD POPULATIONS OF LILIUM CALLOSUM BY PREFERENTIAL SEGREGATION

Abstract

In Lilium callosum fL (a super-numerary chromosome or B-chromosome) shows meiotic drive and tends to increase its number through maternal line transmission. It markedly reduces both pollen and seed fertility when more than one is present. The frequency distribution of fL in natural populations was investigated. The analysis has shown thai individuals with fL are not only less fertile but also less viable. A mathematical theory was developed to analyze the mechanism of distribution of fL in the population. The concept of distortional load (or load due to meiotic drive) was applied to the maintenance of fL in natural populations and it was estimated that this load amounts to about 17 percent. A mechanism was suggested by which the deleterious effect of the fL chromosome may be reduced in the course of evolution.