Gene Mutations 25-4

1. Gene Mutations 25-4

2. GENETICS • Genetics is the study of the transmission of things from one generation to the next • Genetic characteristics of a population can change over time • “Evolution” • These things can be • Traits / characteristics • Chromosomes • Genes

3. GENETIC VARIATION • Genetic variation is produced in two ways • through Mutation • Heritable changes in DNA sequence • Through Gene transfer • Acquiring genes from another member of our species

4. MUTATION • Inheritable change in DNA sequence • Relatively rare • Generally occur during DNA replication or repair • May also occur in response to mobile DNA elements • Transposons and viruses • May affect gene expression

5. SPONTANEOUS MUTATIONS • Occur without effects of outside agents • Radiation, chemical mutagens, etc. • Various types • Base substitutions • One or more base pairs changed • Insertions and deletions • Sometimes caused by transposable elements • Jumping genes • Insertion of one or more bases • Deletion of one or more bases

6. MUTATIONS POINT MUTATION • One base pair altered • Substitution can change the entire reading frame of the DNA causing • Silent mutation – no result because same Amino Acid is produced (lucky there was no change) • Missense mutation • Wrong AA produced which messes up the protein (Sickle Cell Anemia) • Nonsense mutation • Stop command results, so proteins don’t even get made properly

7. Substitution

8. Insertion Mutations

11. MUTATIONS Insertions & Deletion Mutations • “Frameshift mutations” • Insertion or deletion of base pair(s) • e.g., GGA  GAGA (gly  glu) • Generally alter reading frame • “Frameshift” • All downstream amino acids altered • Protein function generally affected • Typically “knockout” mutants

12. Insertion / deletion & genes that jump • “Transposons” = “Jumping Genes” • Transposons are DNA segments spontaneously entering or exiting chromosomes • Transposition into a gene constitutes a large insertion • Gene is generally inactivated • Transposition out of a gene may restore gene function

13. TRANSPOSABLE ELEMENTS • First discovered by Barbara McClintock in the 1940s • Worked with maize (corn) • Kernel color varied as DNA sequences jumped in and jumped out, messing with the pigment genes  no pigment  partial pigment  normal pigment

14. TRANSPOSABLE ELEMENTS • Discovered them in 1940s, but nobody paid attention • Ideas finally accepted in 1970s • Nobel prize in 1983 • She was 81 years old!! • Some of Barbara’s historically significant research plots were destroyed by nutcases protesting genetic engineering • None of the plants were engineered

15. INDUCED MUTATIONS • Some mutations occur spontaneously • Rare • Certain chemicals or radiation can cause mutations • We call these “Mutagens” • Greatly increase the frequency of mutations • e.g., 1,000X or more

16. INDUCED MUTATIONS Chemical Mutagens • Chemicals • Radiation • Ultraviolet • Ionizing radiation(X-rays, gamma rays) • Breaks in single strands • Breaks in double strands • May result in deletions, insertions

17. DNA REPAIR • Mutations are rare • Many errors are automatically corrected by DNA Polymerase’s spell checking abilities • Mutations in genes for DNA repair enzymes are particularly problematic • Increase mutations

18. NORMAL DNA REPAIR • Proofreading is always happening • DNA Polymerase detects error during synthesis • Backs up, excises wrong base, and continues • Relatively accurate • Mismatch repair is completed • Recognizes mismatch if DNA polymerase misses it • Cuts out incorrect segment • Fills in gap correctly • DNA ligase joins the segments • Relatively accurate