How is Genetic Defined?

Not exactly the same as heredity


In the simplest terms, the adjective “genetic” means anything that pertains to a person’s gene sequence that exists within every living cell. Genes are the basic component of heredity in humans and other living organisms.

Genes are made up of DNA, or deoxyribonucleic acid. According to the Human Genome Project – a multinational research endeavor designed to identify and map the genetic sequence of humans – we have an estimated 20,000 - 25,000 genes.

Remarkably, approximately 99% of genes are the same in all people, with the remaining tiny proportion responsible for the differences we see in height, skin color, weight, and other physical traits.

The genetic theory of aging suggests that longevity is also determined by our genes, and some research – such as studies involving identical twins – supports this hypothesis. Other studies have estimated that a person’s lifespan is only about 25% attributable to their heredity, and much more likely to be influenced by lifestyle factors like diet and exercise, and harmful habits like smoking or alcohol abuse.

Further, an emerging field of health science research aims to determine why some genes are "switched on" in the body, and others are not, causing certain physical characteristics or vulnerability to disease, for example.  Called epigenetics, this area of study looks at influencing factors such as maternal stress or environmental exposure, and can at least partially explain why identical twins have physical differences despite possessing the same genetic makeup.

While the term genetic is often used interchangeably with the adjective hereditary, these words don't necessarily mean the same thing.  For example, cancer is a genetic disease in that it involves the genes within a cell (causing that cell to divide uncontrollably), but the cancer itself may be caused by sun or tobacco exposure, and is not necessarily inherited from your parents.


What is a gene? US National Institutes of Health “Genetics Home Reference” Public Information Sheet. Accessed Aug.27, 2012.

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