Genetic approaches to studying common diseases and complex traits.

In a journal published in 2005 by Hirschhorn, complex genetic traits and quantifiable traits like height, weight, cholesterol level in the blood and blood pressure were all linked. The links between these traits were as a result of genetic and non genetic factors. These factors determine whether an individual is susceptible to a common disease. In the journal the author said phenotypes determined the diseases that a person or an individual is most likely to get.
However, the gene that causes phenotype variation in humans cannot easily be found. This is because of how large and complex the human genome is. Therefore, finding an exact set of genes that cause genetic variation is not an easy task. The genomic DNA consists of not only the encoding base pairs but also introns, desert genes and regulatory genes that do not serve any function. Because of this, human genes are made up of unnecessary genes found in thousands of base pairs encoding different proteins. These proteins lead to different gene expressions making it hard to get the gene of interest. The journal does also say that variation in phenotype is not caused by genetic and nongenetic factors but also correlated with the nature of common disease trait that an individual can get. Owing to the complexity of the human genes and the population dynamics, a method “association studies” which requires marking and mapping thousands of nucleotides to indentify a common disease causing gene is expensive and time consuming. It also reduces the chances of getting the right gene responsible for a particular disease and many of these common diseases are linked with patterns in family history as well. And this indicates just how genes determine the susceptibility of an individual being at risk. Common diseases like type 1, 2 and 5 diabetes and quantifiable traits like height, blood pressure and body mass index are heritable. They can be passed from one generation to the other over time and can be indentified by studying one’s family history and studying twins. This is because genetic variation in alleles which are under 1% in a population and in alleles that are higher than 1% in frequency can be used to identify this gene causing variation. However, the author stresses that human population is made of allele frequencies that are more than 5% increasing the likelihood of a common disease in a population. Today, phenotype variation is being used to predict an individual’s chance of getting a disease. Obesity susceptibility for instances can be predicted by determining an individual’s body mass index which is different for individuals due to variation.
With improvements in technology, that might change in the future as different techniques are discovered, modelled and applied.