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Although genes contain all the information an organism uses to function, the environment plays an important role in determining the ultimate phenotype — a dichotomy often referred to as “nature vs. nurture”. The phenotype of an organism depends on the interaction of genetics with the environment. One example of this is the case of temperature-sensitive mutations. Often, a single amino acid change within the sequence of a protein does not change its behavior and interactions with other molecules, but it does destabilize the structure. In a high temperature environment, where molecules are moving more quickly and hitting each other, this results in the protein losing its structure and failing to function. In a low temperature environment, however, the protein’s structure is stable and functions normally. This sort of mutation is visible in the coat coloration of Siamese cats, where a mutation in an enzyme responsible for pigment production causes it to destabilize and lose function at high temperatures The protein remains functional in areas of skin that are colder — legs, ears, tail, and face — and so the cat has dark fur at its extremities.
The dynamic structure of hemoglobin is responsible for its ability to transport oxygen within mammalian blood.
A single amino acid change causes hemoglobin to form fibers.
Environment also plays a dramatic role in effects of the human genetic disease phenylketonuria. The mutation that causes phenylketonuria disrupts the ability of the body to break down the amino acid phenylalanine, causing toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive mental retardation and seizures. If someone with the phenylketonuria mutation is kept on a strict diet that avoids this amino acid, however, they remain normal and healthy
