1. DNA Mutations Chapter 12.4

2. Mutation • Mutation: Any change in a gene is a mutation. • Substances that cause a mutation are called mutagens. • Mutations can also happen spontaneously.

3. Point Mutation • A change in one nucleotide • Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.

4. Point Mutation • Base Substitution - One nucleotide is replaced with another nucleotide. ACC CUA GGC AUC AU ACC UUA GGC AUC AU “C” is substituted with “U”

5. Redundant Systems • Sometimes these mutations have no effect!! Ex. The codons of UCU, UCC, UCA, & UCG all code for the amino acid Serine. Any substitution in the third base of the codon has no effect.

6. However, a substitution in the first or the second base of the codon, changes the code for the amino acid. • UUU codon is for phenylalanine • UCU codon is for serine • CUU codon is for leucine

7. Frameshift Mutations • Either the insertion or a deletion of a nucleotide which results in a shift in the code and mistakes from the point of mutation on. • Original The fat cat ate the wee rat. • Frame ShiftThe fat caa tet hew eer at.

8. Somatic Cell mutations • Mutations happen in all organisms, if it happens in a somatic cell then only the individual is affected.

9. Meiosis Mutations • If it happens in a gamete then the mutation is passed on to the offspring.

10. Meiosis Mutations • Mistakes during meiosis: Mistakes during meiosis, such as non-disjunction, can result in three chromosomes instead of a pair (trisomy) or more than three (polyploidy).

11. Down’s Syndrome • Trisomy in humans can result in birth defects such as trisomy 21, or Down’s syndrome.

12. Quick Review • Point mutations occur as a result of a change in one nucleotide. • The 2 basic types of point mutations are base substitutions and frame shift.

13. Quick Review • Substitution mutations are the result of one nucleotide being replaced by another. This results in one amino acid being incorrectly coded.

14. Quick Review • Frame shift mutations are the result of either a deletion or an insertion of a nucleotide. This results in a mistake in all the triplet codes from the mutation on.

15. Gene Mutations • Gene Mutations occur as a result of changes in chromosomal fragments. There are four basic types: • 1. Translocation • 2. Inversion • 3. Insertion • 4. Deletion

16. Gene Mutations 1.Translocations - When part of one chromosome breaks off and is added to a different chromosome.

17. Gene Mutations 2. Inversion – When part of a chromosome breaks out and is reinserted backwards.

18. Gene Mutations 3. Insertion When part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome.

19. Gene Mutations 4. Deletion When part of a chromosome is left out.

20. Mutations & Evolution • Mutations that have a negative effect usually result in the loss of that mutation due to the law of the survival of the fittest.

23. Mutation & Evolution • However, there are times that the mutations are beneficial and result in the evolution of the species and increased variation in the population. • We’ll learn much more about this next unit!!!