Our understanding of the evolution of DNA content in angiosperm plants has improved in recent years. Genomes in angiosperms vary in DNA content over 1000-fold. Variations in plant genome size are primarily due to differences in ancestral polyploidy and the periodic burst in activity of retroele- ments. Genomic data show a strong correlation between the size of genome and the amount of retroele- ments. Gene duplication have contributed to the functional divergence of the duplicates, and have become a strong evolutionary force.

Nuclear genome size differs thousands-fold in animals and does not correlate with their com- plexity. Such pattern results from domination of non-coding, most often repetitive sequences in genomes. Most common types of repetitive sequences and their origin are mentioned. Then, some hypotheses on the origin of so great variability in the amount of non-coding DNA are presented. According to the present state of knowledge, a cause-and-effect chain exists, from the amount of DNA, through nucleus volume, to cell size.