The genome is the body’s complete DNA, including all of our genes. DNA is a long string made up of four different molecules: adenine (A), thymine (T), cytosine (C), and guanine (G). These molecules (called “nucleotides”) are the chemical building blocks of DNA. Each person's complete DNA sequence is unique, just like a fingerprint.
The human genome is complex, containing around 20,000 genes—small sections of DNA that contain instructions for making proteins, the molecular machinery of life. The proteins coded by the genome carry out numerous tasks in our bodies, from growth and healing to regulating our body temperature. But genes only represent about 1% of our genome; the functions of the remaining 99% of our genome are not yet completely understood and are actively being studied.
.png)
Monogenic diseases
While most diseases stem from a combination of many genes, behaviors, and environmental factors, some rare conditions are caused by a single change in our genetic code. We call these monogenic diseases.
Sickle cell disease is a monogenic disorder that affects red blood cells, causing them to become misshapen due to a single nucleotide change.
Prior to the sequencing of the human genome in 2001, we believed that the genome would provide something like a blueprint or instruction manual for our bodies. However, that turned out to be an oversimplification. The genome has also been referred to as the “information repository” of an organism, but even that may be too simplistic as our understanding of the functioning of the genome evolves. The genome does contain a great deal of information, but so do other parts of the cell—and these cellular components are necessary in some cases for the genome to function.
For example, scientists now know that the activity of a gene is controlled by many external factors, including environmental and behavioral factors. Genes can be turned “on” or “off” depending on various external factors, which has led to the development of the scientific discipline of “epigenetics”. Another surprising outcome from the Human Genome Project was the discovery that very few traits are controlled by individual genes. Rather, most aspects of our biology—from the color of our eyes to the development and progression of chronic diseases like diabetes—are controlled by multiple genes.
How does disease relate to the genome? In some cases, an error (mutation) in a particular gene does greatly increase the likelihood of developing a disease. For example, women who carry a mutation in the BRCA1 gene have a significantly greater risk of developing breast or ovarian cancer. However, despite the strong effect of this particular mutation, not every woman who has it will develop breast cancer; there are still other factors involved. In contrast to the BRCA1 example, most common chronic and age-related diseases—including Type 2 diabetes, cardiovascular disease, obesity and most cancers—are linked to many hundreds or thousands of genes rather than a single mutation. For these “polygenic” conditions, each gene contributes a small amount to the overall risk. And our environment and behavior still have a significant impact on whether that genetic risk will ever be expressed!
While understanding our genome is important for understanding our health, the genome alone does not provide a complete picture. It is therefore important that we take a holistic approach in our exploration of health and disease by looking at what other systems and elements can impact our health picture. Genes are not our destiny. How we interact with the world around us will ultimately determine how healthy and functional our biology is able to be.