Variation in Karyotype and 4C DNA Content in Six Species of Melocactus of the Family Cactaceae

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Analysis of karyotype including somatic chromosome number determination, total chromosome length and volume, estimation of 4C DNA content and Interphase Nuclear Volume (INV) were carried out in 6 species of Melocactus of the family Cactaceae. Somatic chromosome number recorded 2n=22 in Melocactus bahiensis, M curvispinus, M robustispinus, M. townsendii and 2n=44 in M longispinus, M. matanzanus for the first time. Significant interspecific variation in nuclear DNA amount was recorded. The 4C DNA content varied from 20.55 pg in M. townsendii to 40.80 pg in M. longispinus. The correlation coefficient studies showed that the genomic chromosome length, chromosome volume and INV were possitively correlated. No interdependent was found between 4C DNA content and chromosome length or volume and INV. The structural alterations in the chromosomes as well as loss or addition of highly repetitive sequences in the genome showed variations in nuclear DNA at interspecific level indicating a macro- and micro-evolution of the species.