How genetic knowledge can help predict disease risk

SNPs as genetic markers

Geneticists are now able to analyze more than one million SNPs from an individual’s DNA in a matter of days. In recent years, researchers from deCODE Genetics and other institutions have used such information from large groups of individuals to discover SNPs that are associated with characteristics of medical relevance, such as the risk of developing cancer or heart disease. When a SNP is shown to be correlated with such a characteristic, this SNP can be referred to as a genetic marker for the characteristic. Usually, further research is needed to find out whether this SNP or another nearby is the true genetic cause of the characteristic in question. This is not always clear because SNPs that are close to each other on a chromosome tend to be inherited together.

Genotypes and phenotypes

At one level, a genotype is simply a way of referring to different variations of the same gene(s). A genotype is therefore what distinguishes us from one another as individuals both within groups and within the human species. A large collection of genotypes may contribute to the creation of one phenotype. A phenotype is therefore all the observable or tangible elements (size, shape, color and behavior) that could result from a genotype or set of genotypes. However, our phenotype is not entirely dictated by our genes. Environmental factors can also affect our visible traits, either negatively or positively. For example, identical twins share exactly the same genotypes, but may become less identical if subject to different environmental factors, such as diet, climate or levels of exercise.