Organisms used to closely study and elucidate our understanding of basic biological phenomena that might not be easily researched in advanced organisms. In general, they possess characteristics such as small size, short life span and ease of cultivation.
In eukaryotes, the structural unit of the genetic material consisting of a single, linear double-stranded DNA molecule and associated proteins wrapped into a high order structure. During mitosis, chromosomes condense into compact structures visible in the light microscope. In prokaryotes, a single circular double-stranded DNA molecule constitutes the bulk of the genetic material.