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Discover how genes work to make you who you are AND what you can do to maximize what's in your genes. How does DNA carry information? How is this information translated into something useful? What happens when the information changes? What do your food and other lifestyle choices have to do with your genes?

Genes are regions along the DNA molecule that contain information critical to the development and operation of the body. Each gene has a set of instructions. The instructions are in code form and must be translated into proteins that carry out the large number of activities that are essential for life. Some of the proteins are enzymes that assemble or disassemble large molecules or transport food molecules into the body or carry oxygen through the bloodstream. You get the picture - every essential life activity involves proteins. Let's look at the key players in the amazing transition from a chemical molecule, the DNA, to a living, breathing organism such as you!

What is DNA?
DNA (deoxyribonucleic acid) is the genetic material for all living organisms, from the simplest bacterium to the complicated human being. This molecule is fascinating. Within its chemical structure is encoded information that contains the instructions for developing and operating the organism.

DNA has two strands that, when joined together, look like an open spiral staircase. Imagine you're building a house and putting in a spiral staircase. In order for the staircase to fit inside, it's cut down the middle of the steps and then assembled so that the "half - steps" connect in the center. The railings are analogous to the backbone of the DNA molecule. The "half - steps" attached to each railing represent the building blocks of DNA, called "nucleotides". There are four options for each nucleotide, depending on the nitrogen - containing base that's at the heart of the molecule: adenine (A), cytosine (C), guanine (G), and thymine (T). It's common to refer to these bases just by their letters: A, C, G, or T. A pairs with T and G pairs with C to form the steps of the spiral staircase. In fact, they're often referred to as the "genetic letters".

Here's a drawing of what the DNA molecule looks like when it's assembled. Each rung of this DNA ladder represents an A-T or G-C pair.:

In the next section we'll see why the order of the nucleotides is so important.

What is a gene?
Each of the two strands that makes up DNA is a sequence of nucleotides. There are regions within each sequence where the arrangement of nucleotides encodes information, typically for the synthesis of a protein. Proteins are the "worker bees" of the cell and perform a wide variety of activities that are essential to life. A stretch of nucleotides in DNA that code for a protein is defined as a gene . Humans have approximately 25,000 genes.

So where's the info hiding? It's all in the sequence of nucleotides that form the "steps" of the DNA. Each nucleotide within the gene serves as a "genetic letter". When the full gene is read, all the individual letters form words and ultimately a sentence that makes sense: a protein molecule that has a specific task to do within the body.

Although there are only four choices for these genetic letters, they can occur in any order along the sequence of DNA that makes up a gene. It's the order of the letters that ultimately determines the chemical structure of the protein that's made. Can you see how changing even a single nucleotide might affect the protein that's made?

Translating the Information
In order for the information encoded within a gene to be useful, it must first be translated.

The overall process is to convert the information represented by the sequence of nucleotides in the DNA into the amino acid sequence in a protein. Just as nucleotides are the building blocks of the larger DNA molecule, amino acids are the building blocks of proteins.

This decoding process involves an intermediate molecule chemically similar to DNA, called messenger RNA . The "message" that has now been transferred to RNA is moved to the location within the cell where proteins are made. Then translation of the message into a protein takes place. Different arrangements of genetic letters give rise to different proteins. See the diagram Decoding the DNA to follow the process of translating the encoded information into the amino acid structure of a protein.

Decoding the DNA: The Genetic Code Dictates Amino Acid Identity and Order

Image credit: U.S. Department of Energy Human Genome Program, http://www.ornl.gov/hgmis.

Where are genes found?
In complex organisms such as humans, the DNA is found in the nucleus of each of the cells in the body. There are approximately 3 billion nucleotides in human DNA and they're all packed into the tiny nucleus, which is smaller than the head of a pin. If the entire amount of human DNA in one nucleus were stretched to its full length, it would be over 6 feet tall!

What's interesting about where DNA is located is that any cell in the body that has a nucleus (which is all cells except red blood cells) will have a full set of DNA. This is the principle underlying the use of DNA for identification purposes. It's particularly useful for nabbing criminals. Any cells left behind at the scene of the crime - even a single hair bulb - are sufficient to provide DNA that can be used to identify the person whose cells they are. Because each person's DNA is slightly different, each of us has our own unique "genetic signature". It's like leaving your social security number at the scene of the crime!

You can imagine that fitting all that DNA into a nucleus that's so small you can only see it with a high - power microscope requires some special tricks. Much like condensing data so that you can fit more onto your computer's hard drive, DNA is packed tightly into distinct storage units called chromosomes . Humans have 23 pairs of chromosomes. The chromosomes are large enough to be seen under a low-power microscope. Each of the 23 pairs is physically distinct - it has different information (genes) than the other 22 - so, not surprisingly, it's a different size and shape when it's condensed. We have two copies of each of these 23 distinct chromosomes because we inherit one copy from each of our parents.

Each chromosome contains a portion of our total number of genes. A gene has a specific location on a particular chromosome - an "address". This is an important characteristic because it allows researchers to pinpoint the location of a gene and the other genes that it's physically close to. It's also a technical advantage when developing tests for identifying genes or isolating a gene to study the nucleotides in its sequence.

The important facts here are that:

• the nucleus of each cell in our body has a full set of genetic information.
• the information (genes) is divided among 23 chromosomes.
• each chromosome exists as a pair since we receive one copy from each parent.
• each chromosome has a portion of the total 25,000 genes.
• a gene has a specific location or "address" on that chromosome.
• when a cell divides, the new cells get a copy of each of the chromosomes and, thereby, each of the genes on that chromosome.
• all of these characteristics make it possible to inherit genes from our parents (and their parents, etc.) in a predictable manner. It also allows researchers to develop the technology needed to determine what a gene's function is, the impact of variations in a gene on the function of that gene's protein product, and to identify individuals through their genetic signature.

Below is a diagram showing how information hidden deep within our cells is ultimately converted into a protein that then plays an important role in the process of living.

image credit: U.S. Department of Energy Human Genome Program, http://www.ornl.gov/hgmis.

What are gene variants and how do variations in the genes arise?
As critical as the information in DNA is to the body's function, it's not surprising that there are elaborate mechanisms for making sure that our DNA is copied very carefully each time new cells are made. Cell division occurs during periods of growth and development and also during normal cell repair and maintenance. Each time a cell divides every single nucleotide must be faithfully copied so that the information remains unchanged. There's even a proofreading system in place.

However, mistakes happen. The mistake could be major and affect a whole chromosome, which involves many, many genes and the proteins these genes code for. Similarly a mistake may affect a protein that's critically important and cripple its function. It's easy to see how mistakes of this magnitude are likely to have serious effects on the body's ability to function.

There are also mistakes in a single nucleotide or "genetic letter" that have less serious effects on function. The science of personal genetics is concerned with these types of errors and how they affect the way genes and diet and lifestyle choices interact. This type of mistake creates what's called a gene variant, a different version or variation in the usual (more common) form of this gene. As a result, the amino acid sequence of the protein encoded by that gene is affected and the protein's function may change. The protein variation that is made might work better than, the same as, or less well than the original version. An individual having this variation will have a slightly different capability than an individual with the more common version of this gene but the outcome is not a crippling one.

When one of the gene variants is fairly common, defined as occurring in 1% or more of the population, it has a special term: a SNP (pronounced "snip"). SNP stands for s ingle n ucleotide p olymorphism. If you compare two individuals, they'll have the same genes but the DNA sequence of any given gene is likely to be slightly different. These individuals will differ in terms of the SNPs that they have in their DNA. It's these small differences that add up to all of us being humans but distinctly unique. Making even minor changes such as a single nucleotide can lead to variations in outcome, from our physical characteristics, mental capacity, metabolic rate, how we process food molecules or environmental toxins, the rate at which we age to our overall health.

All this discussion leads us to some important points related to personal genetics:

• errors in copying a gene can result in a change in its nucleotide sequence and create a gene variant.
• the protein produced from the variant gene may have a function slightly different from its original one.
• changes in the ability of the protein to do its job can affect the overall functioning of the body positively or negatively.
• humans share the same basic set of genes but differ in the nucleotide sequence within any given gene, called SNPs.
• it's these SNPs that make each person unique from any other person.

See the diagram Effects of Variation in the Sequence of a Gene for a description of how SNPs distinguish individuals.

Effects of Variation in the Sequence of a Gene

image credit: U.S. Department of Energy Human Genome Program, http://www.ornl.gov/hgmis.

Genes and Your Health
Not surprisingly, even minor changes such as gene variants can affect the overall functioning of the body. The impact isn't enough to cause a serious disease but it's definitely enough to impose different requirements on the individual. What's important in the context of personal genetics is how a change affects an individual's nutritional requirements or, the flip side, how an individual responds to components in food.

The first part of this equation involves changes to proteins that are closely involved in using nutrients in food. For example, a gene may code for an enzyme that requires the B vitamin folate. A variation in this gene (ie, a gene variant) contains a nucleotide change in a position along the DNA that ends up changing the structure of it's protein product, which is an enzyme. In this case the structural change affects the ability of the enzyme to bind folate and thereby carry out its critical role in the cells. The structural change results in poor binding of the vitamin. Luckily, supplying a high concentration of this vitamin overcomes the problem. The change handicaps the enzyme and therefore the cells and ultimately the individual but it's a handicap, not a lethal event. By increasing the amount of vitamin in the diet, the enzyme works well and the individual is healthy. However, if the individual with this gene variant does not get sufficient folate, they are at higher risk for developing health problems because poor function of this enzyme has been associated with an increased risk of developing colon cancer, heart disease, and neural tube defects in infants.

There are many, many similar examples in personal genetics of gene variants that result in the potential for health problems if not recognized and compensated for by altering our diet and lifestyle choices. Personal genetics has another equally important focus and that's on how dietary and other lifestyle factors influence how genes express their information. For example, an individual may have a gene variant that produces a protein that promotes chronic inflammation throughout the body. If not detected and allowed to proceed unchecked, the individual may be at risk for increased susceptibility to a number of diseases known to be associated with chronic inflammation. Examples are arthritis, asthma, heart disease, diabetes, cancer, obesity, and inflammatory bowel disorders, to name just a few. From personal genetics research, though, we know that components in food have the power to interact with the genetic material and alter the expression of a number of genes. In this case, omega-3 fats can decrease the expression of pro-inflammatory genes and help this individual reduce their risk of developing chronic inflammation and the diseases known to be associated with this state. Similarly, a gene variant may decrease our ability to dismantle a potentially harmful environmental toxin (eg, tobacco smoke, pesticides) and make us at risk for the damage that such toxins can do to our health. Individuals with such variants have been found to benefit from foods that contain glucosinolates found in members of the cabbage family of vegetables.

The Health or Disease? diagram shows how a single nucleotide change can affect the protein coded for by that gene and alter the functioning of the protein so that these three individuals have slightly different abilities with respect to this protein.

Health or Disease?

image credit: U.S. Department of Energy Human Genome Program, http://www.ornl.gov/hgmis.

These examples give you a sense of the power of personal genetics. When you know which gene variants you have in these key genes, you're armed with information that's critically important to your long-term good health. You're also armed with effective tools for maximizing optimal health because you can then make smart diet and lifestyle choices that will minimize any harmful effects that such variants might cause you.