Environmental influences on phenotype

We have heard that genes and their products do not have isolated action in forming the phenotype. The phenotype develops within the genotype’s limits, depending on the environment. For this interesting matter, I would like to show some amazing examples here. According to Pierce (2008), most discussed characteristics have slight influence from environment. However, many phenotypes have important effect from the environment.

                A curious example is found in the influence of temperature in some gene expressions. In rabbits, the himalayan allele produces dark fur at the relative cool extremities of the body. When rabbits are reared at 20°C or less, this allele expresses the dark pigments in those extremities. When they are reared above 30°C, no dark portions develop. The enzyme responsible for dark fur is not active in higher temperatures. Another example with temperature is observed in some plant’s albinisms. In barley, a plant homozygous for the albino allele has the chlorophyll production inhibited when grown below 7°C. Above 18°C, the same allele expresses green plant with normal chlorophyll. Drosophila melanogaster has also temperature dependent mutation for vestigial wings (Pierce, 2008).

Influence of temperature on allele himalayan expression (Pierce, 2009)

                In humans, we have heard a lot about some environmental effects on health. Obviously, most people who have a fat diet are more likely to get obesity, mainly those who have genetic trend for obesity. Also, more body exposition for U.V. from sunlight influence the emergence of skin cancer. Silverstone and Searle (1970) showed a highly susceptible population from the state of Queensland, in Australia, to get solar keratosis and skin cancer, as the region provides an advantageous environment for these illnesses due to its proximity to the hottest tropic. Weaver (2009) demonstrated the early environment influences on brain development, whose resultant phenotype persists through life. He stated evidences that maternal care in the early postnatal life determine certain gene expressions in the brain through epigenetic modification, shaping the offspring’s neuroendocrine and behavioural stress response throughout life.

REFERENCE LIST

Pierce BA (2008). Genetic Maternal Effect. In: Genetics: A Conceptual Approach. (third edition) W. H. Freeman and Company, New York. pp 123.

Silverston H & Searle JHA (1970). The Epidemiology of Skin Cancer in Queensland: The Influence of Phenotype and Environment. British Journal of Cancer, 24(2): 235–252.

Weaver ICG (2009). Shaping Adult Phenotypes Through Early Life Environments. Birth Defects Research (Part C) 87:314–326.