The Genetic Determinants of Smoking


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The twin studies are an essential subject in understanding the link between nature/nurture or genetic/environment. Basically, the twin study demonstrates how many environmental factors affect an individual’s likely hood of developing a health condition vs genetics factors contributing to the development of health conditions. For example, through the observation of a set of monozygotic twins, we learned that the development of a certain health condition had an environmental factor of 80% and a genetic factor of 20%. This means, adjusting the environmental factor would reduce the efficiency of the disease attack ratio on the twins.

An example of using a twin study to examine the gene-environment interaction is smoking development in monozygotic twins. The method of study will be a case-parent approach study, which is a study that uses the parent as a control. The premises of the examination are a smoking-addict mother giving birth to a set of monozygotic twins. Due to the financial situation, one of the twins was given up for adoption. Over a course of 30 years, these twins were observed to see if gene or environment would contribute to the development of smoking. The methods used to collect data is a phenotypic measure by noting how many cigarettes per day were smoked and a genotype measure of analyzing the gene to see if the twins have a smoking allele received from the mother.

The data showed that through analysis of the gene, the twins had a smoking allele, therefore, the twins had a 30% risk of developing a smoking habit due to the mother’s gene influence. However, twin one who stayed with the mother had an environmental factor of 40%, such as dieting, high-stress levels, and alcohol (similar to the mother), which activated the expression of the smoking gene. Therefore, this individual had an overall 70% risk of smoking, which was due to gene-environment and this twin was smoking 3-4 packs a day between 20-30 years of age. Whereas, twin 2, because of the 30% gene factor and 0% environmental risk factor (not similar to the mother), this individual had an overall 30% risk of smoking, which they did not smoke. However, if twin 2 had environmental factors that affected the gene expression of smoking (similar to the mother), then there would be a higher risk factor of twin 2 smoking.

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