Studies on Nuclear DNA and Meiotic Chromosomes in 8 Species on Mammillaria.

Abstract

Meiotic studies of Pollen Mother Cell (PMCs) and 4C DNA content from root tip cells of 8 species of Mammillaria of the family Cactaceae revealed significant interspecific variations in the genome. The haploid chromosome number n=11 was recorded in M asteriflora, M bella, M. bravoae, M brevispina, M. elongata, M klissingiana and M matudae. The chiasma frequency sig-nificantly varied from 22.25 to 24.28 per nucleus. The formation of univalent in some of the cells, spindle anomalies i.e. early or late separation leads to the formation of pentads, sexads or octads in stead of tetrad formation in the meiotic telophase II through differential pollen sterility from 10.31 to 22.83% in M elongata and M collinsii respectively. The 4C DNA amount of root tip cells varied significantly from 18.262 to 24.124 pg in M klissingiana and M brevispina respectively. Significant variation in DNA amount with gross or minor alteration of chiasma frequency leads to genetic drift among the species.