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  1. GENETIC MUTATIONS Section 5.6 Pg. 259

  2. Mutation: A change in the DNA sequence that is inherited as the DNA is transmitted through cell division.

  3. Categorising mutations • By effect on structure • By consequences on resulting proteins

  4. 1. Mutations by effect on structure • Point mutations • Mutations that occur to a specific base pair in the genome. • Chromosomal mutations • Mutations that involve large segments of DNA.

  5. Point mutations • Substitution: One base pair is replaced with another

  6. Point mutations (cont`d) • Deletion: One or more base pairs is eliminated from the DNA sequence

  7. Point mutations (cont`d) • Insertion: One or more base pairs is inserted into the DNA sequence

  8. Frameshift mutations • Deletions and insertions of 1-2 base pairs will result in a shift in the reading frame. • “frameshift mutations”

  9. Deleting or inserting 3 base pairs is not considered a frameshift mutation... why??

  10. Chromosomal mutations • Inversion :The reversal of a segment of DNA within a chromosome. • Results from breaking and rejoining

  11. Chromosomal mutations (cont`d) • Translocation:A fragment of DNA moves from one part of the genome to another. • Can result in a “fusion protein”

  12. Chromosomal mutations (cont`d) • Gene duplication: Duplication of a coding region of DNA along a chromosome • Results from crossing over of misaligned homologues during meiosis I

  13. Chromosomal mutations (cont`d) • Deletion:Part of a chromosome is deleted and becomes “missing”

  14. Chromosomal mutations (cont`d) • Insertion:The complement of deletion. Part of another chromosome is inserted.

  15. 2. Mutations by consequence on resulting protein • Silent mutations • Missense mutations • Nonsense mutations

  16. Silent mutations • Does not result in a change in amino acid sequence • no phenotypic change; no effect on the cell How? • May occur within an intron • Redundancy of genetic code ACA and ACU are both codons for threonine

  17. Missense mutations • Results in a change to a codon • The wrong amino acid is incorporated • Does not necessarily drastically alter protein function Checkpoint: Can you classify this mutation by its effect on structure?

  18. Nonsense mutations • A codon is converted to a stop codon • truncated protein is produced Checkpoint: Can you classify this mutation by its effect on structure?

  19. Consolidation

  20. Causes of mutations Innate • Spontaneous: Due to errors in replication Environmental • Exposure to mutagenic agents • UV radiation, X rays, chemicals

  21. LEVELS OF GENETIC ORGANIZATION Section 5.8 Pg. 266

  22. Nucleosome • dsDNA is coiled around stabilizing proteins called histones • DNA + histone = nucleosome

  23. Chromatin • Fibrous complex of coiled nucleosomes • In interphase, DNA is in the form of chromatin

  24. Chromosome • During mitosis/meiosis, chromatin supercoils • Supercoiling condenses the strands into chromosomes

  25. DNA composition

  26. DNA composition Coding regions: 5% of genome • 42 000 genes Noncoding regions: 95% of genome • Repetitive DNA • VNTRs (“microsatellites” – genetic markers used in forensics) • Telomeres • Centromeres • Pseudogenes

  27. Homework Mutations: Pg. 263 #1-7