Submitted by: Ellen Burns–Vice President
In dearly every cell of every living organism, there exists a complete set of instructions for creating that organism and regulating its cellular structures and activities over its lifetime. That set of instructions is called a genome.
A genome is organized into distinct, microscopic units called chromosomes. Chromosomes are coiled threads of deoxyribonucleic acid–DNA–that is composed of two long chains of nucleotides bound together in pairs to form a double helix. (A nucleotide is one of the building blocks of nucleic acids, such as DNA. A nucleotide is made up of three parts: a base, a sugar, and a phosphate. The bases lie flat like steps of a staircase. The sugar and phosphate form the backbone of the nucleic acid. DNA is composed of four different kinds of nucleotide.)
Three and a half billion of these nucleotide pairs make up the human genome.
Specific sequences of nucleotide bases within a DNA strand–called genes–are the cells’ instructions for producing proteins. Scientists estimate that 80,000 to 100,000 of these basic units of heredity exist within the human genome. Proteins perform a wide variety of physiological tasks. They facilitate processes such as digestion, breathing, immune responses, the production of heat and energy, and the movement of fluids in and out of cells.
While most members of a species have the same collection of genes, each individual’s unique characteristics stem from slight variations–called polymorphisms–in the sequence of nucleotides that comprise the genes of that individual. On average, the DNA of any two individuals will differ by about 0.1 percent.
Other types of variations–called mutations–also occur. Both polymorphic and mutagenic variations may be harmful to an individual by inhibiting the production, or altering the normal function, of protein. Most diseases result from these types of genetic variations.
The goal of genomic inquiry is to identify the sequence of nucleotides, understand the function of every gene they comprise, and clarify the genetic variations that define individuality and create disease.
Credit: www.celera.com–Celera Genomics