[priyasaravanan_1406]

The gene expression is determined by two features called as penetrance and expressivity of the genes. Penetrance is the ratio of individuals exhibiting expected phenotype and expressivity is the extent of gene expression in an individual. The phenotype of an individual is determined by the genotype or the type of gene expressed. In general, phenotypic changes occur in individuals when exposed to various environmental factors. But the query, “Is the genotype of an individual is influenced by external environment?” lead to several researches throwing light on the effect of external or environmental factors like temperature, light, chemicals and nutrition in gene expression. Besides the effect of internal factors like hormones and metabolism on gene expression, external factors were also found to affect the gene expression and ultimately exhibiting phenotypic changes.

Temperature and Gene Expression: The study on the coat color of the Himalayan rabbit with relation to the temperature reveals the effect of temperature. The rabbit with normal phenotype of white fur showed differences in the skin color with exposure to temperature. The body of the rabbit which is generally exposed to high temperature (>34 degrees) expressed white color whereas the other parts like ears, nose , tail and paws which are little exposed to temperature expressed black color. Keeping the rabbit under cold climate resulted in the expression of fully black colored skin. This study proves the sensitivity of the genes responsible for the skin color to the temperature.

Another study on wing development in Drosophila flies with response to the temperature also provided results with the effect of temperature. Flies exposed to the temperature of 25 degree Celsius showed less penetrance whereas when exposed to higher temperature penetrance also increased which was observed by the increase in the development of wings in the selected population of flies.

The research by the scientist Voolstra CR and his team from KAUST, Saudi Arabia on studying the gene expression by exposing the embryos of Coral Montastraea faveolata to different temperatures like 27.5, 29 and 31.5 degree C resulted in the continuous expression of stress related genes in the embryos that were exposed to 31.5 degree C. Also the effect of temperature on genes encoding the enzyme for the biosynthesis of starch in the wheat plant Triticum aestivum was studied by William J Hurkman and his co-workers from USDA, USA. The effect of temperature on these genes was observed by analyzing the starch accumulation.
Also the research on the effect of temperature reduction on gene expression and oxidative stress in skeletal muscle from adult Zebra fish by Ranae L and team and the study of sea water acidification and elevated temperature’s effect on gene expression pattern of the Pearl Oyster Pinctada fucata by Wenguang Liu and team, China shows the role of temperature, an external environmental factor on gene expression.

Light and Gene Expression: The study of a gene responsible for the anthocyanin pigment formation in Maize plant with relation to the light by researchers is a good example showing the role of light in gene expression. The plant carrying the homozygous gene for pigmentation when exposed to sun light developed bright red color and when the light was retarded by covering the area of the plant prone to pigmentation, the bright red phenotype was not observed. Also the prevalence of skin cancer in humans on exposure to sunlight is a classic example.

Chemicals and gene expression: The research by Mankame T and team from Texas University on a fungicide called Enable which has potential effect on endocrine regulated gene showed down regulation of 8 genes and upregulation of 34 genes on exposure to the chemical. The effect of chemical mutagens and carcinogens on gene expression profiles in human TK6 cells by the researcher Lode Godderis and his team developed results. In their experiment, they observed a linear trend in Dose- response of gene expression for chemicals like Trichloroethylene, Benz(a)anthracene, epichlorohydrine, benzene and hydroquinone. The effect of the sedative drug Thalidomide on fetus causing birth defects can also be coined as an example for the effect of chemicals.

Nutrition and Gene Expression: It is a very interesting fact that dietary and nutritional supplement also plays an important role in gene expression. The deficient nutrient supplement alters the genetic expression. What a pregnant woman eats determines the health of her offspring. Babies born with deformities to mother ingested with Thalidomide drug during 6th week of pregnancy in 1960s should be cited. The folic acid supplement to the pregnant women takes care of the development of the fetus whereas the deficiency of the same causes some birth abnormalities.

Thus the fact that the environmental factors also play a vital role in gene expression is understood by various research studies.