Genetic information is physically carried on large DNA strings that are organized into chromosomes. Each species is characterized by a chromosome set that carry the information necessary and sufficient for its development and survival. Eukaryotic organisms are mostly diploid, containing two sets of chromosomes with each pair carrying nearly identical genetic information. Occasionally, exceptions to this rule are found, such as haploid yeast (with only one set of chromosomes) or polyploid ferns and frogs (with multiple sets). Nevertheless, the composition of chromosome set remains identical within a species
