HER - Environmental Effects [LESSON]
Environmental Effects
Human phenotypes—and phenotypes of other organisms—also vary because they are affected by the environment. For instance, a person may have a genetic tendency to be underweight or obese, but his or her actual weight will depend on diet and exercise (with these factors often playing a greater role than genes).
One striking example of how the environment can affect phenotype comes from the hereditary disorder phenylketonuria (PKU). People who are homozygous for disease alleles of the PKU gene lack activity of an enzyme that breaks down the amino acid phenylalanine. Because people with this disorder cannot get rid of excess phenylalanine, it rapidly builds up to toxic levels in their bodies. If PKU is not treated, the extra phenylalanine can keep the brain from developing normally, leading to intellectual disability, seizures, and mood disorders. However, because PKU is caused by the buildup of too much phenylalanine, it can also be treated in a very simple way: by giving affected babies and children a diet low in phenylalanine. If people with phenylketonuria follow this diet strictly from a very young age, they can have few, or even no, symptoms of the disorder. In many countries, all newborns are screened for PKU and similar genetic diseases shortly after birth through a simple blood test.
Phenotypic plasticity occurs when the same genotype is expressed in different ways in different environments. Phenotype changes can be in an organism's behavior, morphology, or physiology in response to an environmental factor that affects its survival. For example, red-eyed tree frogs lay egg clutches that take in important information from the vibrations felt around them. They use it to determine whether or not to hatch early and make a quick escape from predations.
Watch the Phenotype Plasticity video created by the Khan Academy below.
Environmental factors influence many genetic traits, both directly and indirectly. An organism's ability to adapt to the local environment reflects a flexible response in its genome. Cells can control what genes are turned on and off in response to internal and external conditions. Specific DNA-building proteins interact with the environment and other proteins to determine what genes should be copied in transcription and expressed in translation. We’ll learn more about how this works in the next module.
Learn more about Environmental Effects by clicking the image and then clicking the arrow button at the bottom of the activity.
A really neat example of environmental effects on phenotype is the production of vitamin D in different skin colors. It’s a delicate balance between UV protection and UV absorption necessary to produce vitamin D.
Check out this Skin Color video about the arising of different tones of skin colors based on intensity of UV radiation in different parts of the world.
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