Genetics

Mutations of Genes 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  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 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

Figure 7.20 Effects of Mutation

Figure 7.9 Genetic Code

mutations 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

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

Mutagens  Radiation  Ionizing radiation (x-rays) – induces breaks in chromosomes  Nonionizing radiation (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

Figure 7.24 DNA Repair

Figure 7.24 DNA Repair

Identifying Mutants, Mutagens, and Carcinogens  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

Genetic Recombination and Transfer 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 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

Transformation 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

Figure 7.29 Griffith’s Experiments

Figure 7.30 Generalized Transduction

Specialized transduction

Figure 7.31 Bacterial Conjugation

Figure 7.31 Bacterial Conjugation

Figure 7.32 Bacterial Conjugation

Transposons and Transposition 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)

Transformation 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

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

Transfer of Genetic Information 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