The Evolution of Basikaryotypes in <i>Scilla permixta</i> with Special Reference to the Genome

Abstract

The karyotypes of the offspring of Scilla permixta, the II type (2n=15=B1B2), were analyzed from the view point of the differentiation or, the evolution of basikaryotype. The B1 with 8 chromosomes is the most primitive one from which the B2 with 7 chromosomes seems to be derived by elimination of the St3 chromosome. In this form a new sat-chromosome Mt4 originates by translocation of a satellite to the M4 chromosome. The B3 seems to be formed from the B1 by translocation of the St3 chromosometo the distal end of the Ma chromosome. Another sat-chromosome M34 with secondary constriction appeared in this form.When three different sat-chromosomes are differentiated from the St3 sat-chromosome of the B1, basikaryotypes with two sat-chromosomes such as B4 and B5 may be differentiated, and the occurrence of hasikaryotype with threee sat-chromosomes such as B6 may be expected in-the offspring of the individual no. 1. The process of the differentiation of the basikaryotype started from the B1, through B2, B3, B4 and B5 finally to the B6 is clearly demonstrated: the seven chromosome types in the basis are derived from the eight chromosome type, and two and three sat-chromosome types are derived from one sat-chromosome type.The present observation of the differentiation of basikaryotypes contributes to the conception of the genome which implies the necessary and well-balanced genes for the viability and is altered in its balance gradually in the process of the evolution.In conclusion the writer's hearty thanks are due to Prof. Sinoto of the Tokyo Imperial University for his kind advice in the course of this investigation.