What is a genome?

Each of us contains many slight variations in our genomes that make us unique. Most of these variations have little or no impact on our health. But that’s not always the case.

Sometimes if a DNA letter is missing or wrong in a gene’s instructions, it may produce a damaged protein, extra protein or no protein at all. Such changes in genes are called genetic mutations.

Genetic mutations can cause serious health problems because they affect proteins, which are the workhorses of your body. For example, proteins form special scaffolds that help your cells keep their shapes. They serve as enzymes that help your stomach digest food. The molecule that carries oxygen in your blood is a protein, as are estrogen, testosterone and other hormones.

The transmission of genetic mutations from one generation to the next helps to explain why many diseases run in families. If a certain disease runs in your family, doctors say you have a family history of the condition.  

What IS a genome?

There are more than 6 billion people on our planet — each a massive collection of about 100 trillion cells.

How do these cells know what to do? What tells them to work together to keep your heart pumping, brain thinking and bones growing? The answer lies in a long, winding molecule called deoxyribonucleic acid, or DNA.

The DNA contained within each of your cells carries the instructions needed to build and maintain the many different types of cells that make you, you. Researchers call this complete set of DNA instructions a “genome.”

Is my genome unique?

Humans come in many shapes and sizes, but we’re all very similar at the DNA level. In fact, the genomes of any two people are more than 99% the same.

Still, the tiny fraction of the genome that varies among humans is very important. DNA variations are part of what makes each of us unique. They affect the color of your eyes, hair and skin. What’s more, they influence your risk of disease and your response to drugs.

So, is everything determined by my genome?

No, your DNA is just one part of the amazing puzzle of who you are. When it comes to your health, other pieces of the puzzle include lifestyle and environmental factors, such as the food you eat and the air you breathe. Once we learn more about how the human genome interacts with these factors to cause disease, we may be able to change our habits and adapt our environment to improve our health. Our genomes also are likely to contribute to some of the ways we feel, think and act. But keep in mind that many other things, such as how you were raised and your access to medical care, can influence your behaviors and your health.

What does my genome do?

If you could peer inside your cells, you’d see your genome contained in 46 tightly packed bundles of DNA — 23 came from your mother and 23 from your father. These DNA bundles, called chromosomes, provide the instructions that enable a one-cell embryo to develop into a 100 trillion-cell adult.

But DNA isn’t just about growth. It instructs cells throughout your life — telling them how to respond to the foods you eat, the germs you encounter and the pollutants to which you are exposed. Ultimately, DNA even influences how you age.

To understand DNA’s instruction manual, let’s look at its structure. If you unwind the DNA molecule packed into each chromosome, it looks like a twisted ladder. The rungs of this ladder are made from four types of chemical building blocks. These blocks — adenine, thymine, cytosine and guanine — are abbreviated with the letters A, T, C and G.

Depending on how many of these building blocks are stacked together and the order in which they are arranged, DNA can produce many different types of organisms.

It takes about 3 billion pairs of A’s, T’s, C’s and G’s to write the instructions needed to build a human. So, every time the human body produces a sperm or an egg, 3 billion DNA letters must be copied and packaged so they can be passed along to future offspring.

Information from:

National Human Genome Research Institute (2007, Oct). A Guide To Your Genome. NIH Publication No. 07-6284. Retrieved from: www.genome.gov.

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