DNA Mutations

1. DNA Mutations

2. Objectives • Contrast gene mutations with chromosomal mutations

3. Mutations • What is a mutation? • Any change in a DNA sequence • What causes mutations? • errors in replication, transcription, cell division, or by external agents

4. Mutations in Reproductive Cells Affects: • Changes the sequence of nucleotides within a gene in a sperm or an egg cell • If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring

5. Mutations in Reproductive Cells Affects continued: • A new trait may be produced • May result in a protein that does not work correctly • Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive • In some rare cases a gene mutation may have positive effects

6. Mutations in Somatic Cells • What happens if powerful radiation, such as gamma radiation, hits the DNA of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone? • If the cell’s DNA is changed, this mutation would not be passed on to offspring • However, the mutation may cause problems for the individual

7. Mutations in somatic Cells • Damage to a gene may impair the function of the cell • When that cell divides, the new cells also will have the same mutation • Some mutations of DNA in body cells affect genes that control cell division • This can result in the cells growing and dividing rapidly, producing cancer

8. 2 Major Types of Mutations • Point mutation • involves a change in only 1 base • Frameshift mutation • one or more bases are inserted or deleted

9. Point Mutations • Substitutions • One base is changed to another base • Like incorrectly writing a single letter in a sentence: THE APE SAW THE DOG BEG THE APE SAW THE DOE BEG Circle the substitution on your notes!

10. What will happen? • A substitution will cause either a single amino acid change or no change at all. • Remember that many different codons can code for a single amino acid • If GAU changes to GAC due to a mutation, the resulting amino acid will still be aspartic acid

11. mutated base Effects of Point Mutations

12. Frameshift Mutations • Insertion • One or more bases are added into the DNA sequence THE APE SAW THE DOG BEG THE APE SAE WTH EDO GBE G • Deletion • One or more bases are removed from the DNA sequence THE APE SAW THE DOG BEG THE APE SAT HED OGB EG

13. What will happen? • A frameshift mutation will shift every base after the mutation, thus affecting every amino acid after the mutation

14. So What? • When the sequence of DNA bases changes, the resulting mRNA from transcription will be different. • If the mRNA is different, the amino acid sequence could be affected.

15. Deletion Insertion Substitution

16. Genetic Mutations Chromosomal mutations —involve changes in the number or structure of chromosomes • Deletion • Loss of all/part of chromosome • Duplication • Segment of chromosome is repeated • Inversion • Part of chromosome is reversed of its usual direction • Translocation • Part of one chromosome breaks off and attaches to another non-homologous chromosome

17. Deletion Duplication Inversion Translocation Chromosomal Mutations Deletion Duplication Inversion

18. Causes of Mutations • Spontaneous: • Some mutations just happen • Ex: a mistake in the base pairing during DNA replication • Most are caused by Environmental Factors • Ex: radiation, chemicals, and even high temperatures

19. Repairing DNA • Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides • These repair mechanisms work extremely well, but they are not perfect • The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will not be corrected