Nucleotides are important components of a DNA strand. Each nucleotide is made up of a phosphate group, a sugar, and a chemical base (see images 1 and 2). In DNA, there are four possible bases: adenine (A), thymine (T), guanine (G) and cytosine (C). These are the chemicals that make up genes, the body’s instructions.
The bases on a DNA strand pair up with the bases on the opposite strand, and are coiled together to form the double helix. There are rules to this base pairing: adenine pairs up with thymine, and cytosine pairs up with guanine. The entire human genome has about 3 billion of these base pairs.
What are Single Nucleotide Polymorphisms?
An SNP (pronounced “snip”) is a variation in one nucleotide base. For example, the sequence AAGGTT may change to become AAGGTC. In humans, SNPs are the most common type of genetic variation. SNPs don’t change much through generations, meaning they are stable enough to be studied.
There are thought to be around 10 million SNPs in the human genome. Most of the genome sequence doesn’t code for anything, and the majority of SNPs are found in these non-coding areas. Those found in coding areas are more likely to have an effect on gene function, which can impact health and development.
Why is it Useful to Study Single Nucleotide Polymorphisms?
As technologies have improved, so has SNP detection. But why study them at all? SNPs may be useful for:
- Determining how an individual will respond to certain drug treatments.
- Determining if an individual is at risk for developing certain diseases. This includes consideration of environmental factors, such as the effects of viruses and toxins.
- Identifying genes associated with complex diseases such as cancer and diabetes.
- Determining how disease genes are passed from one generation to the next.
- Assessing the effects of non-genetic factors on health and development, such as diet and lifestyle.
- Genetic marking of the genome. SNPs can act as biological markers, allowing more accessible navigation of genome maps.
To learn or revise some basic genetics concepts, read Basic Cell Biology for Understanding Genetics and Introduction to Terminology Used in Genetics. For more information on SNPs, including details of some of the groups involved in SNP research, read the SNP Fact Sheet page on the Human Genome Project Information website.
Sources
“Genomic Research”, published: 17th May 2010, Genetics Home Reference website, accessed: 5th June 2010, no author specified.
“SNP Fact Sheet”, last modified: 19th September 2008, Human Genome Project Information website, accessed: 5th June 2010, no author specified.
“SNPs: variations on a theme”, revised: 20th September 2007, National Center for Biotechnology Information website, accessed: 5th June 2010, no author specified.
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