Blue eyes or brown? Short or tall? Blond, redhead, or brunette? All the information that guides development of physical traits as well as the other aspects of the human body is encoded in long sequences of deoxyribonucleic acid (DNA). Sections of DNA, known as genes, tell the body how to develop and function. The human genome is made up of about three billion building blocks called nucleotides, which code for around 20,000 genes located on 23 chromosomes. Humans have two copies of each chromosome and thus two copies of each gene. Each parent donates one copy of a gene– one from the mother and one from the father.
Figure 1: The Central Dogma of Biology was coined by Francis Crick in 1953 to illustrate the flow of genetic information. First, DNA is used as a template to create a complimentary strand of ribonucleic acid (RNA) through a process called transcription. This RNA template is then used to create a protein by stringing together amino acids in a process called translation.
Genes consist of specific DNA sequences which use four different nucleotides: adenine (A), cytosine (C), guanine (G), and thymine (T). The DNA sequence is used to create protein via a two- step process, transcription and translation (Figure 1). The resulting protein performs the function coded by the gene.
Figure 2: A SNP is a change in the genetic code of an individual where a single nucleotide is replaced by another in the DNA sequence. Nucleotides: adenine (A), cytosine (C), guanine (G), and thymine (T).
Of the three billion nucleotides that make up the human genome, the majority (~99.7%) remain the same from person-to-person. The remainder can vary in a number of different ways. The most common variation is a single nucleotide polymorphism (SNP – pronounced ‘Snip’). A SNP occurs when a nucleotide at a specific position in the DNA sequence gets replaced with a different nucleotide (Figure 2). Thus far, approximately 10 million SNPs have been identified. Most SNPs are found in non-protein coding regions of DNA. However, SNPs in sections coding for genes can result in changes to the transcription/translation process. This can result in a slightly different protein, which may not function in the typical manner.
In some cases, individuals may never notice the change in the protein function. In others, the change could lead to symptoms such as anxiousness, poor bone health, and reactions to various environmental stimuli. Identification of SNPs in specific genes for use in guiding lifestyle and treatment choices to improve overall health and wellness is known as Functional Genetics.
Guest author: Curtis Christian is a member of the Clinical Support & Education Department at NeuroScience, Inc. and the resident expert in genetics.
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