Our genes affect every aspect of our lives, from the way we look to the diseases we get. However, they don't act in an isolated manner, because we are also affected by the environment we live in. Our diet, exercise levels, pollution levels in the place we live – all affect what happens to our bodies. For example, major diseases such as cancer and coronary artery disease are caused when multiple genes start to malfunction, but lifestyle and environmental factors also play a major role in shaping these disorders and their severity. Since many factors are involved scientists call these types of inheritance as 'Multifactorial Inheritance'. These diseases impact a large proportion of the population, so it is important to understand how these diseases are inherited and how they can be minimized through lifestyle changes.
Scientists examine the relative roles of genes and the environment by using methods that make intuitive sense. To look at the genetic effects, they examine a patient's family, who share the gene pool. If many close relatives are affected, there exists a strong possibility of a genetic component to the disease. For example, if both twins in an identical pair are affected by a disease, but only some of their siblings, and just few cousins then it is strong evidence that the disease is genetic. This is because identical twins have nearly the same genes; their siblings have about half of the same genes and cousins, about one-eighth. As the percentage of shared genes decreases, the chances of having a genetically determined disease also decreases. With recent developments in both gene sequencing and bioinformatics, scientists have been able to study these diseases in much greater detail. DNA sequencing is a direct method to examine genes at the root level within families and the larger population. It allows scientists to identify the exact genes responsible and to helps better predict disease and inheritance patterns. With this information doctors and genetic counsellors can advice changes in lifestyle that can result in longer healthier lives for patients and the general population.