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Transcript
Classify the following genetic disorders as being caused by addition mutation, deletion mutation, or substitution mutation. For the substitution mutations, give the normal and abnormal DNA and mRNA base sequences, as well as the normal and abnormal amino acid coded for by those base sequences. 1. In one patient with cystic fibrosis , a C is changed to a T at nucleotide 1609. This converted a (CAG) to a (TAG). The protein produced by this patient had only the first 493 amino acids of the normal chain of 1480 and could not function. 2. Sickle cell anemia is an inherited condition. People with sickle cell anemia inherit two copies of the sickle cell gene, one from each parent. The sickle cell gene makes abnormal hemoglobin, called Hemoglobin-S. In sickle cell anemia, the abnormal hemoglobin (Hemoglobin-S) sticks together when it gives up its oxygen to the tissues. These clumps cause red blood cells to become stiff and shaped like a sickle. It takes two copies of the sickle cell gene for the body to make the abnormal hemoglobin found in sickle cell anemia; thus sickle-cell is an autosomal recessive trait. In sickle-cell anemia, the replacement of A by T at the 17th nucleotide of the gene for the beta chain of hemoglobin changes (GAG) to (GTG). 3. In the most common form of PKU(phenylketonuria), a TCC is changed to a ACC, resulting in an inactive enzyme and incomplete metabolism of phenylalanine-containing compounds such as proteins. The resulting buildup of phenylalanine can cause mental retardation, eczema, loss of skin pigmentation, and other disorders. If detected early, the disease is treatable by excluding foods high in phenylalanine form the diet. 4. The replacement of C by U resulting in the formation of UAG in place of CAG in codon number 39, and a shortened globin chain containing only 39 instead of the normal 146 amino acids in the -globin protein chain produces a protein that is functionally useless and gives clinical symptoms of thalassaemia, which results in a low red blood cell count (anemia) as well as Fatigue and weakness, Pale skin or jaundice (yellowing of the skin), Protruding abdomen with enlarged spleen and liver, Dark urine, Abnormal facial bones and poor growth, A poor appetite, and delayed puberty in adolescents. 5. Dystrophin is a protein that is an important component of skeletal muscle. The dystrophin gene is located on the long arm of the X chromosome. It is a very large gene spanning 2.5 million bp of genomic DNA and codes for a protein of approximately 3600 amino acids (11kb). removal of the whole or most of the dystrophin gene during DNA replication results in Duchenne muscular dystrophy. This is a severe X-linked recessive disorder that affects boys and is transmitted by carrier females. In affected boys there is almost complete lack of dystrophin, muscle weakness beginning in childhood and increasing progressively in severity so that the individual is wheel-chair bound at the age of about 15 years. Death usually ensues in the early twenties due to respiratory muscle involvement. 6. Removal of a small, non-critical part of the dystrophin gene results in altered dystrophin that causes the clinical condition of Becker muscular dystrophy in which muscle weakness begins in adolescence and is very slowly progressive, and affected individuals may lead an almost normal life. 7. Hemophilia A is an X-linked, recessive, bleeding disorder caused by a deficiency in a protein factor that causes blood-clotting. Affected individuals develop a variable phenotype of hemorrhage into joints and muscles, easy bruising, and prolonged bleeding from wounds. This condition can result from a mutation in which CGA is converted to TGA or when CGA is changed to CAA in the gene that codes for the clotting factor. 8. Tyrosinase-positive oculocutaneous albinism (OCA, type II) is an autosomal recessive disorder in which the biosynthesis of melanin pigment is reduced in skin, hair, and eyes. Although affected infants may appear at birth to have a complete absence of melanin pigment, most patients with OCA type II acquire small amounts of pigment with age. Individuals with OCA type II have the characteristic visual anomalies associated with albinism, including visual problems and is caused by removal of one or more segments of gene that result in melanin production. 9. A four nucleotide insertion in the gene that codes for the protein fibrillin results in TaySachs disease, which is an autosomal recessive genetic disorder. In its most common variant, known as infantile Tay–Sachs disease, it causes a relentless deterioration of mental and physical abilities that commences around six months of age and usually results in death by the age of four.