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Mutations

Mutations. Mutations. mutations – errors in the DNA can have a bad resultant effect can have no effect can have a positive resultant effect Mutations are usually not an issue because we have two copies of each gene. Mutations. Changes in DNA result in: silent mutations

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Mutations

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  1. Mutations

  2. Mutations • mutations – errors in the DNA • can have a bad resultant effect • can have no effect • can have a positive resultant effect Mutations are usually not an issue because we have two copies of each gene.

  3. Mutations Changes in DNA result in: • silent mutations • missense mutations • nonsense mutations

  4. Silent Mutations • silent mutation – has no effect on the function of the cell; sequence of amino acids is not affected • often found in the non-coding (regulatory) regions • third NT of codons can be changed yet still code for the same amino acid

  5. Missense Mutation • missense mutation – nucleotide sequence is changed such that a different amino acid is coded for • protein function may or may not be affected Sickle cell anemia is a result of a missense mutation.

  6. Sickle Cell Anemia

  7. Nonsense Mutations • nonsense mutation – nucleotide sequence is changed such that an amino acid is replaced with an early stop codon • short proteins are made; usually digested by proteases • nonsense mutations usually are lethal

  8. Type of DNA Change:Point Mutations • point mutation – nucleotide changes where one base pair (bp) is replaced by another bp Point mutations are also known as substitution mutations.

  9. Type of DNA Change: Frameshift Mutation • frameshiftmutations – changes in the DNA sequence which modify the translation reading frame • Deletions– removal of one or more NTs • Insertions– addition of one or more NTs

  10. Type of DNA Change:Chromosomal Mutations Sections of chromosomes can break off and reattach abnormally. • Translocation mutations • Inversion mutations

  11. Chromosomal Mutation • translocation mutations – large portions of DNA are exchanged

  12. Translocation

  13. Down Syndrome

  14. Chromosomal Mutations • inversion mutations – sections of a chromosome are reversed

  15. Crossing Over

  16. Fixing Mutations

  17. Fixing Mutations Enzymes are able to recognize when: • nitrogenous bases are missing • nitrogenous bases are fused together These mutations are detected and fixed by DNA polymerase I.

  18. Fixing Mutations Enzymes recognize when bases are incorrectly paired together. These mismatch mutations are fixed by DNA polymerase III. How does the enzyme know which strand has the correct base pair? The original template strand is methylated.

  19. Causes of Mutations

  20. Causes of Mutations • spontaneous errors due to enzymes • induced errors due to mutagenic agents • UV radiation • X-rays • chemical (Agent Orange) • transposable elements

  21. Spontaneous Errors • guanine may react with water to form 8-oxo guanine • 8-oxo G pairs up with adenine during replication

  22. Visualization of Mutations

  23. Transposable Elements • some DNA sequences naturally move themselves around the genome - transposons

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