Genome size

When it became clear that a bigger genome does not imply a greater number of genes, these questions arose:

- Why are some genomes much bigger than others?
- What is the extra DNA?
- What is the function (if any) of the extra DNA?

Gene number is well conserved between related species. So in those species with the larger genomes, gene density must decrease. Much of the extra DNA appears to consist of repetitive elements.