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Genetics

Genetics. Mutation – change in the nucleotide base sequence of a genome; rare Not all mutations change the phenotype Two classes of mutations 1. Base substitution eg point mutation G TTCAAG - wild type (normal) A TTCAAG - mutant (abnormal) Silent mutation

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Genetics

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  1. Genetics

  2. Mutation – change in the nucleotide base sequence of a genome; rare • Not all mutations change the phenotype • Two classes of mutations • 1. Base substitution • eg point mutation • GTTCAAG - wild type (normal) • ATTCAAG - mutant (abnormal) • Silent mutation • No change in amino acid sequence Mutations of Genes

  3. Missense mutation • New amino acid • ALA-PHE-LEU-TRY-STOP • PHE-PHE-LEU-TRY-STOP • Non-sense mutation – a stop codon is inserted into protein sequence • Truncated protein • Worse than missense Mutations of Genes

  4. 2. Frameshift mutation • Insertion or deletion of one or more bases • ATT GCC AGG TAA (convert to mRNA) • ATG CCA GGT AA_ • Worst type of all types of mutations • If it happens at the end of a gene it may not be as bad Mutations

  5. Effects of Mutation Figure 7.20

  6. Genetic Code Figure 7.9

  7. Missense mutation eg. sickle cell • results in a codon that codes for a different amino acid. The resulting protein may be nonfunctional • Nonsense mutation eg Cystic fibrosis • Stop codon,truncated protein • Frameshift insertion eg. Tay-Sachs disease • Frame shift deletion CCR5 • Both cause a shift in the reading frame mutations

  8. Spontaneous • Happens during replication More often in prokaryotes than eukaryotes eukaryotes have better repair mechanisms Causes of mutations

  9. Radiation • Ionizing radiation (x-rays) – induces breaks in chromosomes • Nonionizingradiation (UV light) – induces thymine dimers • Chemical Mutagens • Nucleotide analogs – disrupt DNA and RNA replication and cause point mutations • Eg. 5-bromouracil pairs with guanine • Caffeine not a strong mutagen – effect fetal development • Alkylating agents- used for cancer treatment Mutagens

  10. DNA Repair Figure 7.24

  11. DNA Repair Figure 7.24

  12. Mutants – descendents of cell that does not successfully repair a mutation • Wild types – cells normally found in nature • Methods to recognize mutants • Positive selection • Survival of the fittest • Negative (indirect) selection • selective removal of rare alleles that are deleterious. Ames test assess the mutagenic potential of chemical compounds Identifying Mutants, Mutagens, and Carcinogens

  13. Exchange of DNA segments composed of homologous sequences • Recombinants – cells with DNA molecules that contain new nucleotide sequences • Vertical gene transfer – organisms replicate their genomes and provide copies to descendants • Horizontal gene transfer – donor contributes part of genome to recipient; three types • Transformation • Transduction • Bacterial Conjugation Genetic Recombination and Transfer

  14. Exchange of DNA segments composed of homologous sequences • Recombinants – cells with DNA molecules that contain new nucleotide sequences • Vertical gene transfer – organisms replicate their genomes and provide copies to descendants • Horizontal gene transfer – donor contributes part of genome to recipient; three types • Transformation • Transduction • Bacterial Conjugation Genetic Recombination and Transfer

  15. Transforming agent was DNA; one of conclusive pieces of proof that DNA is genetic material • Cells that take up DNA are competent; results from alterations in cell wall and cytoplasmic membrane that allow DNA to enter cell Transformation

  16. Griffith’s Experiments Figure 7.29

  17. Generalized Transduction Figure 7.30

  18. Specialized transduction

  19. Bacterial Conjugation Figure 7.31

  20. Bacterial Conjugation Figure 7.31

  21. Bacterial Conjugation Figure 7.32

  22. Segments of DNA that move from one location to another in the same or different molecule • Result is a kind of frameshift insertion • Transposons all contain palindromic sequences at each end • Simplest transposons are insertion sequences which have no more than two inverted repeats and gene for transposase • Complex transposons contain one or more genes not connected with transposition (e.g. antibiotic resistance) Transposons and Transposition

  23. Transforming agent was DNA; one of conclusive pieces of proof that DNA is genetic material • Cells that take up DNA are competent; results from alterations in cell wall and cytoplasmic membrane that allow DNA to enter cell Transformation

  24. Genotype – set of genes in the genome • Phenotype – physical features and functional traits of organism Gene Function

  25. Transcription – information in DNA is copied as RNA nucleotide sequences • Translation – polypeptides synthesized from RNA nucleotide sequences • Central dogma of genetics • DNA transcribed to RNA • RNA translated to form polypeptides Transfer of Genetic Information

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