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Human Genetic Mutations 2 Main Types of Mutations 1.) Chromosomal Mutations 2.) Gene Mutations What are chromosomes? • Humans have 23 pairs of chromosomes, with one chromosome from each parent. • The chromosomes are coiled up DNA. • Under normal conditions all of the chromosomes are inherited in tact. 5 Types 1. 2. 3. 4. 5. Deletion Duplication Inversion Translocation NonDisjunction Chromosomal Deletion One or more genes are removed Causes: Wolf-Hirschhorn syndrome (severe mental retardation) cri du chat syndrome (mewing sounds, mental retardation) Chromosomal Duplication A segment of genes is copied twice and added to the chromosome Causes: Charcot–Marie–Tooth disease (high arched foot, claw feet, confined to a wheelchair) Chromosomal Inversion a segment of genes flip end-to-end on the chromosome Causes: Four-Ring Syndrome (cleft pallate, club feet, testes don’t descend) Chromosomal Translocation Material is swapped with another chromosome Causes: Burkitt’s Lymphoma (cancer of the lymph nodes, in children) Nondisjunction • Chromosomes FAIL TO SEPARATE during meiosis • Meiosis I Nondisjunction • Meiosis II Nondisjunction Nondisjunction • Produces gametes (and therefore a baby) with one missing chromosome or one extra chromosome Nondisjunction (in Meiosis II) Fertilization Nondisjunction • Every cell in that baby’s body will have __ copies of this chromosome instead of___. • This condition is called ____________. • Trisomy 21 = Individual has _____ copies of chromosome # ________ Nondisjunction • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called __________. • Trisomy 21 = Individual has _____ copies of chromosome # ________ Nondisjunction • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called TRISOMY • Trisomy 21 = Individual has __ copies of chromosome # ____. Nondisjunction • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called TRISOMY • Trisomy 21 = Individual has 3 copies of chromosome # 21. Trisomy 21 - Down Syndrome Gene Mutations: 2 Types Point Mutation Frameshift Mutation Point Mutation • One base (A, T, C, or G) is substituted for another • Causes: ex. - Sickle-cell anemia • 3 Possible Consequences: – nonsense mutations: code for a stop, stops the translation of the protein – missense mutations: code for a different amino acid – silent mutations: code for the same amino acid Example: Sickle Cell Anemia Normal Red Blood Cell • Red blood cells shaped like a disc • Hemoglobin (protien) carries oxygen to all parts of the body Sickle Red Blood Cell • Red blood cells form an abnormal crescent shape • Hemoglobin (protein) is abnormally shaped • don't move easily through your blood vessels • form clumps and get stuck in the blood vessels Frameshift Mutations • They shift the “reading frame” of the genetic message. – May change every amino acid that follows the point of the mutation. – Can alter a protein so much that it is unable to perform its normal function. Frameshift Mutation • One or more bases (A, T, C, or G) are added or deleted • Causes: Ex. Cystic Fibrosis • Caused by: – Insertion: adding a base – Deletion: removing a base Frameshift Mutation • Original: –The fat cat ate the wee rat. • Frame Shift (“a” added): – The fat caa tat eth ewe era t. Causes of Mutations • spontaneous • occur during DNA replication • Caused by MUTAGENS • physical, ex: radiation from UV rays, X-rays or extreme heat • or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA). Significance of Mutations • Many, if not most, mutations are neutral • Harmful mutations are the cause of genetic diseases • Some mutations, however, are beneficial and lead to a more diverse gene pool.