Genomics is an area within medical science that examines the ‘genome’ - the complete set of genetic information you have which determines how your body functions and what it looks like. In order to understand genomics, it is important to know what genes are and what they do.
The cell is the basic building block of all living things. Your body is made up of billions of cells which contain genetic information – the instructions for how your body should grow and function. This genetic information is stored in DNA (deoxyribonucleic acid), a chemical molecule shaped in a double helix.
DNA is made from a series of chemicals called bases, represented by the letters A, T, C and G (adenine, thymine, cytosine, guanine), which are joined one after another in a long chain. The order or sequence of the bases in a DNA strand forms the genetic code. Particular stretches of the genetic code are called genes, and each gene is a specific instruction to the body. For example, a gene may be an instruction about eye colour. You usually have two copies of each gene, one inherited from each of your parents.
Inside a cell, DNA is packaged into structures called chromosomes. There are usually 23 pairs of chromosomes in each cell (46 in total). Nearly every cell in your body has the same DNA, and the entire amount of DNA in the cell is called the genome.
Sometimes it can be useful to think of the genome as a book, where each of the chapters represents a chromosome. Sentences in these chapters would be the genes and the letters that make up each word can be considered the DNA bases.
A 'spelling mistake' in a sentence or gene might mean that the gene doesn’t function properly. A mistake in your genetic code might lead to something not happening in your body the way it should.
What is the difference between genomics and genetics?
Genetics is the study of one particular gene and its effects. Genomics is genetics on a larger scale: the study of your genome, your complete set of DNA, including all your genes.
A genetic test usually looks at one or a small number of genes at a time. A genomic test is a new type of test that can capture information from a large number or all of your genes at the same time. This means doctors may have a better chance of finding gene changes causing or associated with your disease or condition.
We can now do tests to examine a section of the DNA ‘sentence’ for changes that may alter its meaning and lead to disease.
Use of the three images above is with permission from the National Society of Genetic Counselors (US). Citation: This project was made possible through the National Society of Genetic Counselors and a grant from the Audrey Heimler Special Project Award.
How are genes involved in disease? What is a genetic disease or disorder?
Genetic conditions arise due to an alteration in one or more of your genes. If you have a version of a gene which doesn’t work as it should, you might be born with or develop a disease, depending on what role that gene plays in your body. Gene variations are often inherited – passed on from one generation to the next. Examples of some of the better-known inherited genetic disorders are Huntington’s Disease and Cystic Fibrosis. Genetic tests are used to diagnose these disorders.
Do all gene variations lead to disease?
More than 99% of the genome is the same in all humans. The changes or variants in the DNA sequence of a gene might change the way that gene works. Some variants in the genome are commonly found throughout the population, and some are rare. Some gene variants have no effect on your health, however, other variants may affect your health, your responses to particular medications or cause genetic conditions.
For more information on genetic conditions and genomic testing, see Resources for Participants.