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Transcript
Human Genetic Diseases Genetic Disease Song http://www.youtub e.com/watch?v=g qvYOr78THo&feat ure=related Simple Recessive Heredity Most genetic disorders are caused by recessive alleles. Cystic fibrosis Cystic fibrosis (CF) is a fairly common genetic disorder among white Americans. Cystic fibrosis Approximately one in 28 white Americans carries the recessive allele, and one in 2500 children born to white Americans inherits the disorder. Due to a defective protein in the plasma membrane, cystic fibrosis results in the formation and accumulation of thick mucus in the lungs and digestive tract. Tay-Sachs disease Recessive disorder of the central nervous system Results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system. Because this lipid fails to break down properly, it accumulates in the cells. Typical Pedigree for Tay-Sachs I 1 2 II 1 2 3 4 1 2 III 3 IV 1 Phenylketonuria Also called (PKU) A recessive disorder that results from the absence of an enzyme that converts one amino acid, phenylalanine, to a different amino acid, tyrosine. Because phenylalanine cannot be broken down, it and its by-products accumulate in the body and result in severe damage to the central nervous system. Phenylketonuria A PKU test is normally performed on all infants a few days after birth. Infants affected by PKU are given a diet that is low in phenylalanine until their brains are fully developed. Ironically, the success of treating phenylketonuria infants has resulted in a new problem. Phenylketonuria If a female who is homozygous recessive for PKU becomes pregnant, the high phenylalanine levels in her blood can damage her fetus—the developing baby. This problem occurs even if the fetus is heterozygous and would be phenotypically normal. Phenylketonuria Phenylketonurics: Contains Phenylalanine Huntington’s disease Huntington’s disease is a lethal genetic disorder caused by a rare dominant allele. It results in a breakdown of certain areas of the brain. Huntington’s disease Ordinarily, a dominant allele with such severe effects would result in death before the affected individual could have children and pass the allele on to the next generation. But because the onset of Huntington’s disease usually occurs between the ages of 30 and 50, an individual may already have had children before knowing whether he or she is affected. Typical Pedigree of Huntington’s Disease I 1 2 II 2 1 4 3 5 III 1 2 3 4 5