Genes are the basic blueprints that tell our bodies how to grow and develop. They are made up of deoxyribonucleic acid (DNA). The individual molecules of DNA are called nucleotides, and they are strung together in a double, twisted thread.
There are four nucleotides that exist in complementary pairs; adenine with thymine, and cytosine with guanine. They are usually referred to by their first initials only, ATGC. The pattern of ATG and C is called a DNA sequence, and the process of examining each nucleotide in a laboratory is called sequencing.
Each combination of three nucleotides matches to an amino acid. During cell functions, complex groups of proteins move along the DNA strand, “reading” the nucleotides, creating strings of amino acids to make proteins and enzymes.
Genes are organized into exons and introns. Exons are the only part of the gene that create, or “express” protein. Introns are intervening pieces of DNA that are discarded during the protein creation process.
Genes are carried on chromosomes, which are tightly wound threads of DNA and a stabilizing element called histone. We inherit half of our chromosomes, and therefore half of our genes from our mother, and the other half from our father. The chromosomes are found in the nucleus of the cell.
We have other DNA, too, in the mitochondria. Mitochondria are important in energy production in the body, and are only inherited from our mothers.
All the DNA content of an individual, including chromosomes and mitochondria, is called the genome (“Genetics Glossary” Retrieved from https://www.kumc.edu/gec/glossnew.html#G ; Finegold, 2013).
As new cells are created, including when the eggs and sperm are made in the reproductive organs, errors can be introduced into chromosomes or DNA. An error at the DNA level is commonly known as a “mutation,” but currently the preferred term is “variant.” Historically it was easier for researchers to find gene variants that caused rare, severe disease and disability.
These are referred to as genetic disorders because a gene variant is the primary cause of the disease (“Genetics Glossary” Retrieved from https://www.kumc.edu/gec/glossnew.html#G ; Finegold, 2013). There are over 4,000 described genetic disorders (“Online Mendelian Inheritance of Man” Retrieved from http://omim.org/).
Examples of Genetic Disorders:
•Sickle Cell Disease
•Tay Sachs Disease
•Duchenne Muscular Dystrophy
With the advent of new technologies that have made it easier to explore the genome, gene variants have been identified that are common and pre-dispose individuals to common, chronic disease. These variants are called single nucleotide polymorphisms (SNPs).
There are over 11,000 SNPs associated with seventeen different disease areas. In common chronic disease, SNPs are only one risk factor. The environment in which one lives, including lifestyle, plays an important role as well in the development of certain diseases.
Examples of Diseases Influenced by SNPs and Environment:
Research has gone beyond disease and now genetics can provide information about muscle strength, response to exercise and strength training, and how one metabolizes carbohydrates, vitamins, and fats. Genetic tests are now available on the market that can help individuals identify their pre-disposition to common diseases, and develop intervention strategies that are personalized to their individual needs.