SNP(Single Nucleotide Polymorphism)

Recently, I’m studying Genetics and there is an important concept called SNP, or Single Nucleotide Polymorphism, in my first project. Since SNP is very important for understanding human gene, I would like to make a brief introduction to it.

What is SNP? In a word, SNP is the key to make two people different from each other in genetic level. As we know, gene determines everything of life, such as our body shape, hair color, etc. Since different people have different phenotype, it is natural to think that different people have different genes. However, our human genes are not that different as we think. As a matter of fact, most part (99.9%) of human gene sequence is exactly the same, and only a small portion of human genes are different from each other, and we call these different portions of genes the SNPs.

Human gene is long sequence that is comprised of 3 billion nucleotides(A G C T). For every two individual people, there is only one difference in 1000 nucleotides, so there are 3 million SNPs between two people. Recent study suggests that there may be more SNPs than we previously know, that is there is one SNP in every 300 nucleotides. Here is an example of SNP: for 90% percent of people, there is a sequence ATGCCCGT in our second chromosome. However, the sequence of the corresponding part for the rest 10% people is ATGCACGT (the fifth nucleotide changed from C to A).

A example of SNP among 3 people

SNPs are the keys to understand the function of gene and area hot research area in bioinformatics. For example, by compare the SNPs between normal people and the color-blind people, we will hope fully discover which part of gene is responsible for color-blind and then find a way to cure the disease by changing that piece of DNA.

The bad news of SNPs is that is not easy to discover the influence of the changes in DNA sequence. The main reason is that there is along and complicated way for changes in DNA to cause changes in protein.In fact, SNPs need to cause the change of amino acid first, and then a slightly change in amino acid will trigger a sharp change in the structure of protein. Here is a picture to briefly explain the genetic process inside our body that start from DNA and you can image what will happen if the very beginning of DNA is changed.