The Relationship Between Cytomixis, Chromosome Mutation and Karyotype Evolution in Lily

Abstract

SUMMARYSpontaneous intercellular chromatin migration (cytomixis) occurred in PMCs of Lilium davidii at synizesis stage of meiosis, and less frequent in later stages. This process has led to the formation of up to 9.44% to 13.6% of PMCs, microspores, and generative cells with chromosome numbers deviating from the normal haploid chromosome complement, n= 12. The abnormal cells contained chromosome numbers ranging from 8 to 15. The patterns of intercellular chromatin migration may be divided into two types: (a) The chromatin substance may migrate from one nucleus into one adjacent cell, and (b) from one nucleus into two or more cells or from two or more nuclei into one cell. According to the chi-square test, it has been shown that the differences between the patterns of intercellular chromatin migration and the variation of chromosome number in the PMCs, microspores or generative cells are not significant. Because of cytomixis, about 10% cells proved to be aneuploids, with hypoploids predominating. It shows that the descending basic number is greater than that of the ascending. This is in accordance with the principle of the trend in karyotype evolution—the progressive reduction of the basic chromosome number. If these newly established karyotypes are survived by rigorous selection, they may be expected to accomplish fertilization and thus give rise to aneuploid progeny in a population. It is these selected chromosome mutations which may be of considerable evolutionary significance.