Question

It is sometimes argued that one’s phenotype is “all in their genes.” Yet, this is only partially true. What other factors contribute to an individual’s phenotype? For instance, while someone might be genetically predisposed to developing lung cancer, what other broad categories of factors might contribute to the occurrence of disease?

Answer 1

Two factors that influence an individual's phenotype are: (1) the specific genetic information of the individual (its genotype), and (2) environmental influences on the expression of the individual's genetic potential. The observation that genetically identical organisms often vary greatly in phenotype clearly shows that gene-environment interaction is indeed an important regulator of phenotypic variation, including variation related to a number of diseases. Scientists have long appreciated the role that environmental factors play in the production of traits in animals. Environmental factors such as diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens can all impact which of an animal's genes are expressed, which ultimately affects the animal's phenotype. Nevertheless, even genetically identical organisms exposed to controlled experimental conditions can have different phenotypes, pointing to the power of subtle environmental differences on gene expression. Studies have shown that there is a specific point in the development of certain organisms, known as the thermosensitive period (TSP), during which the gonadal tissue is responsive to temperature. When exposed to one range of temperatures, this tissue develops into ovaries; when exposed to a different range, it develops into testes. Such is the case in the turtle Emys obicularis: at incubation temperatures of 25°C, all such turtles are born male, but at temperatures of 30°C, all are born female.

The broad categories of factors that contribute to lung cancer are explained below:

1. Smoking is by far the leading risk factor for lung cancer. About 80% of lung cancer deaths are thought to result from smoking and this number is probably even higher for small cell lung cancer (SCLC). It’s very rare for someone who has never smoked to have SCLC. The risk of lung cancer for smokers is many times higher than for non-smokers. The longer you smoke and the more packs a day you smoke, the greater your risk. Cigar smoking and pipe smoking are almost as likely to cause lung cancer as cigarette smoking. Smoking low-tar or “light” cigarettes increases lung cancer risk as much as regular cigarettes. Smoking menthol cigarettes might increase the risk even more since the menthol may allow smokers to inhale more deeply.
2. If you don’t smoke, breathing in the smoke of others (called secondhand smoke or environmental tobacco smoke) can increase your risk of developing lung cancer.
3. Radon is a naturally occurring radioactive gas that results from the breakdown of uranium in soil and rocks. WE can’t see, taste, or smell it. According to the US Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer in this country, and is the leading cause among non-smokers. Outdoors, there is so little radon that it is not likely to be dangerous. But indoors, radon can be more concentrated. Breathing it in exposes your lungs to small amounts of radiation. This may increase a person’s risk of lung cancer.
4. People who work with asbestos (such as in mines, mills, textile plants, places where insulation is used, and shipyards) are several times more likely to die of lung cancer. Lung cancer risk is much greater in workers exposed to asbestos who also smoke. It’s not clear how much low-level or short-term exposure to asbestos might raise lung cancer risk. Other carcinogens (cancer-causing agents) found in some workplaces that can increase lung cancer risk include: Radioactive ores such as uranium, Inhaled chemicals such as arsenic, beryllium, cadmium, silica, vinyl chloride, nickel compounds, chromium compounds, coal products, mustard gas, and chloromethyl ethers, Diesel exhaust
5. People who have had radiation therapy to the chest for other cancers are at higher risk for lung cancer, particularly if they smoke. Examples include people who have been treated for Hodgkin disease or women who get chest radiation after a mastectomy for breast cancer. Women who have radiation therapy to the breast after a lumpectomy do not appear to have a higher than expected risk of lung cancer.
6. In cities, air pollution (especially near heavily trafficked roads) appears to raise the risk of lung cancer slightly. This risk is far less than the risk caused by smoking, but some researchers estimate that worldwide about 5% of all deaths from lung cancer may be due to outdoor air pollution.