Genetic diversity exists within human population

Genetic polymorphism, the occurrence in a population of multiple forms of a particular DNA region, confers diversity to human population. Single-nucleotide polymorphism (SNP) is particularly abundant throughout human genome and populations. A SNP could lie within or outside a gene region.

SNPs could affect gene function

Though most SNPs are inert, different alleles or forms of a SNP could have a small effect on the phenotype, or outward manifestation of a gene. For example, the presence of ABO blood types is the result of having 3 alleles of the same gene (called ABO gene). In addition, different alleles may have different level of functional efficiency. Thus, which allele we inherit from our parents could have an impact on our cellular biochemistry, physiology and health.  

SNPs and disease risk

Many SNPs have been shown to be associated with the risk of developing diseases. For instance, XRCC1, a gene functions in DNA repair possesses a SNP in codon 399 that encodes either an arginine (Arg) or a glutamine (Gln). In human population, the Gln-allele is less abundant than the Arg-allele, we thus call Gln-allele a minor allele. The Arg- allele repairs damaged DNA more efficiently than the Gln-allele. Thus, carriers of Arg-allele accumulate fewer DNA damage than carriers of Gln-allele. Consequently, studies found that Arg-allele carriers are less susceptible to cancer than Gln-allele carriers.

SNPs generally do not directly cause a disease, but merely alter the risk of developing a disease. There are many of these disease-associated SNPs, and the minor alleles of these SNPs either increase or reduce the risk of developing diseases. By analyzing the genotypes of a collection of these SNPs, we may predict the likelihood that an individual will develop a specific disease or physiological condition, for example cancers or high blood cholesterol, in his/her lifetime. This type of risk assessment is termed predisposition test.

• Genetics in Brief

• Genetic Polymorphisms and Predisposition to Diseases

• Genetic Mutations and Inherited Disease

• Genetics and Response to Medical Treatment

• Genetics and Disease Prognosis

• Unlocking the Secret of Human Genome

◊ DNA Sequencing
◊ Microarray