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GENETIC MUTATIONS

GENETIC MUTATIONS. Section 5.6 Pg. 259. Mutation : A change in the DNA sequence that is inherited as the DNA is transmitted through cell division. Categorising mutations. By effect on structure By consequences on resulting proteins. 1. Mutations by effect on structure. Point mutations

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GENETIC MUTATIONS

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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

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