Genome size variation and basic chromosome number in pearl millet and fourteen related Pennisetum species

Abstract

A systematic analysis of Pennisetum species has shown their cytological variability for basic chromosome number (x = 5, 7, 8, and 9), ploidy level, and chromosome size. We have identified the genome size and base composition of 15 species using flow cytometric procedure in order to test the relationship of these characters with the variation in basic chromosome number and to evaluate the ascendant dysploidy hypothesis from an ancestral x = 5 group. Ethidium bromide, bisbenzimide Hoechst 33342, and chromomycin dyes have been used for genome size, percentage of AT, and percentage of GC nucleotides determination, respectively. Results show that genome sizes are variable among the Pennisetum species. This variation appears to be negatively related to the basic chromosome number. On the contrary, genome size is not correlated with percentage of GC. This result shows that loss or gain of DNA that has occurred during evolution within this genus seems not to be especially associated with GC- or AT-rich sequences.