1. 8.7 – Mutations

2. Key Concept  Mutations are changes in DNA that may or may not affect phenotype. mutated base

3. 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

4. Are Mutations Helpful or Harmful?  Mutations happen regularly  Almost all mutations are neutral  Chemicals & UV radiation cause mutations  Mutagens are anything in the environment that can cause mutations  Many mutations are repaired by enzymes

5. Are Mutations Helpful or Harmful?  Some types of skin cancers and leukemia result from somatic mutations  Some mutations may improve an organism’s survival (beneficial)

6. Types of Mutations

7. Chromosome Mutations  May Involve:  Changing the structure of a chromosome  Loss or gain of part of the chromosome

8. Chromosome Mutations  Five types exist:  Deletion  Inversion  Translocation  Nondisjunction  Duplication

9. Deletion  Due to breakage  A piece of a chromosome is lost

10. Inversion  Chromosome segment breaks off  Segment flips around backwards  Segment reattaches

11. Duplication  Occurs when a gene sequence is repeated

12. Translocation  Involves two chromosomes that aren‘t homologous  Part of one chromosome is transferred to another chromosome

14. Nondisjunction  Failure of chromosomes to separate during meiosis  Causes gamete to have too many or too few chromosomes

15. Nondisjunction  Can cause “ Trisomy ” ( three copies of the same chromosome in an egg or sperm)  Trisomy 21 (Down syndrome)

16. Chromosome Mutation Animation

18. 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.

19. Types of Gene Mutations  Include:  Point Mutations  Substitutions  Insertions  Deletions  Inversions  Frameshift Similar to the chromosomal versions of these mutations

20. Point Mutation  Change of a single nucleotide  Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

21. Point Mutation  Sickle Cell disease is the result of one nucleotide substitution  Occurs in the hemoglobin gene

22. Nonsense Mutation  Type of point mutation  Results in a premature stop codon and usually a nonfunctional protein

23. Frameshift Mutation  Inserting or deleting one or more nucleotides  Changes the “ reading frame ” like changing a sentence  Proteins built incorrectly

24. Frameshift Mutation  Original:  The fat cat ate the wee rat.  Frame Shift (“a” added):  The fat caa tat eth ewe era t.

25. Amino Acid Sequence Changed

26. Gene Mutation Animation

27. Silent Mutations  Some mutations have no effect and are called “silent”  Example:  GUC changed to GUG  Both code for the amino acid valine  This would not affect the protein being made in any way

28. Mutations may or may not affect phenotype.  Chromosomal mutations tend to have a big effect.  Some gene mutations change phenotype by:  causing a premature stop codon.  causing a change in protein shape or the active site.  causing a change in gene regulation.

29.  Some gene mutations do not affect phenotype.  A mutation may be silent because…. –It occurs in a non-coding region. –It may not affect protein folding or the active site.