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MUTATIONS Learning Objectives • • • Define mutations Enlist various types of mutations Justify their role in disease causing process What Are Mutations? • • • Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring Are Mutations Helpful or Harmful? • • • • Mutations happen regularly Almost all mutations are neutral Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes Are Mutations Helpful or Harmful? • • Some type of skin cancers and leukemia result from somatic mutations Some mutations may improve an organism’s survival (beneficial) MUTATIONS • Defined as PERMANENT change in DNA Levels: • • GENE MUTATION: (may, and often, result in a single base error) CHROMOSOME MUTATION: (visible chromosome change) GENOME MUTATION: (whole chromosome) GENE MUTATION • • DELETION OF A SINGLE BASE SUBSTITUTION OF A SINGLE BASE GENE MUTATION • • • • POINT MUTATION within a coding sequence: VAL-GLU MUTATIONS in NON-coding sequences defective transcription, regulation DELETIONS/INSERTIONS “frameshift” mutation, involvement is NOT a multiple of 3 Tri-nucleotide REPEATS, e.g., CGG repeats many times in fragile X syndrome. GENE MUTATIONS • • • • • INTERFERE with protein synthesis SUPPRESS transcription, DNARNA PRODUCE abnormal mRNA DEFECTS carried over into TRANSLATION ABNORMAL proteins WITHOUT impairing syntheses Types of Mutations Chromosome Mutations • May Involve: – Changing the structure of a chromosome – The loss or gain of part of a chromosome. Chromosome Mutations • Five – – – – – types exist: Deletion Inversion Translocation Nondisjunction Duplication Deletion • • Due to breakage A piece of a chromosome is lost Inversion • • • Chromosome segment breaks off Segment flips around backwards Segment reattaches Duplication • Occurs when a gene sequence is repeated • • Translocation Involves two chromosomes that aren’t homologous Part of one chromosome is transferred to another chromosomes Translocation Nondisjunction • • • Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Disorders: – Down Syndrome – three 21 chromosomes – Turner Syndrome – single X chromosome st – Klinefelter’s Syndrome – XXY chromosomes Chromosome Mutation Animation Gene Mutations • • • Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc. Types of Gene Mutations • Include: – Point Mutations – Substitutions – Insertions – Deletions – Frameshift Point Mutation • • • • Change of a single nucleotide Includes the deletion, insertion, or substitution of ONE nucleotide in a gene. Point Mutation Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene Frameshift Mutation • • • Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly. Frameshift Mutation • • Original: – The fat cat ate the wee rat. Frame Shift (“a” added): – The fat caa tet hew eer at. Amino Acid Sequence Changed Gene Mutation Animation Reference • Basis Pathology by Robbins