NUCLEAR-DNA CONTENT AND CHIASMA BEHAVIOR IN 6 SPECIES OF GYMNOCALYCIUM PFEIFF OF THE FAMILY CACTACEAE

Meiotic studies including chiasma frequency determination of Pollen Mo ther Cells (PMCs) and 4C DNA content from root tip cells of 6 species of Gymnocalycium of the family Cactaceae revealed significant interspe cific variation in the genome. The haploid chromosome number n=11 was recorded in G, bruchii, G. denudatum, G, horridispinum, G, mihanovichi i, G. quehlianum and G. saglionis. The chiasma frequency significantly varied from 30.45 to 34.28 per nucleus. The formation of univalent in some of the cells, spindle anomalies i.e. late or early separation le ads to the formation of pentads, sexads or octads instead of tetrads f ormation in the meiotic telophase II through differential pollen steri lity from 2.83 to 7.31% in G. mihanovichii and G. saglionis respective ly. The 4C DNA amount of root tip cells varied significantly from 12.0 21 to 14.661 pg in G. saglionis and G. bruchii respectively. Significa nt variation in DNA amount with gross or minor alteration of chiasma f requency leads to genetic drift among the species.