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GeneticDisease211S - Mutation and Genetic Diseases 1...

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Mutation and Genetic Diseases - 1 Effects of Mutation on Protein Function and Genetic Diseases As mentioned in our inheritance section, many human diseases are the result of mutations, often leading to non-functional alleles. The effect of such mutations if the altered allele is expressed is an altered protein. Mutations can result in enzymes that do not function, abnormal protein structure or changes in protein conformation that result in a non-functioning or differently functioning protein. The effect of mutations is often expressed in the way in which genes and the environment interact, which, under the "right" conditions, may cause disease or make an individual more susceptible to disease. This complex interaction of the genotype and the environment means that much of our "normal" health is genetically influenced, including our susceptibility to chronic health diseases such as cardiovascular disease, hypertension, diabetes and cancers. These health issues for humans that may have both genetic and environmental components are multifactorial. It should not be surprising that many genetic diseases are "caused" by recessive alleles. A mutation in one allele so that it can no longer code for the correct protein can be masked in the phenotype if the unaffected allele on its homologous chromosome can still code for sufficient enzyme or other gene product. It is difficult to remove recessive alleles from the population when individuals who are heterozygous have the altered allele but do not exhibit the problem. In human inheritance, individuals who are heterozygous for a genetic "disorder", but do not exhibit symptoms are called carriers. Carriers can pass the allele to the next generation. Mutations that are always expressed as dominant alleles have greater impacts when harmful to the individual hence are less common in the human population. We will look at some effects of mutation in the context of human genetic diseases.
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Mutation and Genetic Diseases - 2 The Effect of Mutation on Enzyme Function Mutations in DNA that lead to non-functional or dysfunctional enzymes are among those now readily detected through genetic screening tests ( see later ) . If the enzyme is critical for survival, affected homozygous recessive individuals will die if there is no treatment available. Some human genetic diseases caused by enzyme-coding genes include: Galactosemia: the inability to convert galactose to glucose in the liver. Phenylketonuria: the inability to process the amino acid, phenylalanine. Lactose Intolerance: the inability to digest lactose to glucose and galactose. Tay-Sachs Disease: the inability to produce critical brain cell lysosome lipases. Tay-Sachs is fatal in early childhood. About 1 in 28 Ashkenazi Jews in the United States are Tay-Sachs carriers.
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