10.1 Genetic Material Possesses Several Key Characteristics

Life is characterized by tremendous diversity, but the coding instructions of all living organisms are written in the same genetic language—that of nucleic acids. Surprisingly, the idea that genes are made of nucleic acids was not widely accepted until after 1950. This skepticism was due in part to a lack of knowledge about the structure of deoxyribonucleic acid (DNA). Until the structure of DNA was understood, how DNA could store and transmit genetic information was unclear. Even before nucleic acids were identified as the genetic material, biologists recognized that, whatever the nature of the genetic material, it must possess four important characteristics.

• 1. Genetic material must contain complex information. First and foremost, the genetic material must be capable of storing large amounts of information—instructions for the traits and functions of an organism.
• 2. Genetic material must replicate faithfully. A second necessary feature is that genetic material must have the capacity to be copied accurately. Every organism begins life as a single cell. To produce a complex multicellular organism like yourself, this single cell must undergo billions of cell divisions. At each cell division, the genetic instructions must be transmitted to descendant cells with great accuracy. When organisms reproduce and pass genes on to their progeny, the coding instructions must be copied with fidelity.
• 3. Genetic material must encode the phenotype. The genetic material (the genotype) must have the capacity to be expressed—to code for traits (the phenotype). The product of a gene is often a protein or an RNA molecule, so there must be a mechanism for genetic instructions in the DNA to be copied into RNAs and proteins.
• 4. Genetic material must have the capacity to vary. The genetic information must have the ability to vary, because different species and even individual members of a species differ in their genetic makeup.