Consider these not-so-random samples from the animal world: a cockroach, a zebrafish, a mouse. What do these creatures have in common? Left to right: American cockroach (Periplaneta americana), zebrafish (Danio rerio), house mouse (Mus musculus). Cockroach image from Wikimedia Commons, zebrafish and mouse from Wellcome Images. Well, they're all animals and that means they're all eukaryotes, for example. They all have DNA-based genomes.