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genetics chapter 7
mutations
| Question | Answer |
|---|---|
| forward mutation | change from wild type allele to mutant allele, changing the phenotype of the organism |
| reversion | mutations that cause a mutant allele to change back to a wild type allele |
| substitution | when a base at a certain position in the DNA strand is replaced by one of the other 3 bases. |
| transition | one purine replaces the other purine, or one pyrimidine replaces the other pyrimidine |
| transversion | purine changes into a pyrimidine, or vice versa |
| insertion | the addition of one or more nucleotide pairs |
| deletion | the block of one or more nucleotide pairs is removed from the DNA molecule |
| spontaneous mutation | random changes in the DNA sequence that arise from errors during normal cellular processes, such as DNA replication, and are not caused by external mutagens |
| does the mutation rate differ for different genes? | yes it does; it can range from less than 10^-9 to more than 10^-3 per gene per gamete |
| does the mutation rate differ for different organisms? | yes, the average mutation rate in generation to generation in multicellular eukaryotes is higher than that of bacteria |
| does the mutation rate differ for oocytes and sperm? | yes, sperm contain more mutations than oocytes because more rounds of cell division are needed for sperm than eggs |
| depurination | the hydrolysis of a purine base from the DNA backbone |
| deamination | the removal of an amino group in a nitrogenous base |
| how does UV light cause mutations? | it cause two adjacent thymine residues to be chemically linked, forming thymine dimers, as well as oxidative damage to the other bases |
| proofreading | Polymerase molecules provide a proofreading function in the form of a nuclease that becomes active whenever the polymerase makes a mistake. |
| how do trinucleotide repeats cause mutations | if there are trinucleotide repeats beyond a certain number, it results in a disease causing allele |
| mutagen | any physical or chemical agent that rises the frequency of mutation above spontaneous rate |
| base analog | compounds that mimic DNA nucleotides but have minor structural differences |
| intercalators | flat molecules that can sandwich themselves between successive base pairs and disrupt the machinery for replication, generating deletions or insertions of a single base pair. |
| what is the ames test and how does it work? | This test asks whether a particular chemical can induce Histidine+ (His+) revertants of special Histidine- (His-) mutant strains of the bacterium Salmonella typhimurium. |
| how are mutates bases repaired? | base excision repair for minor base damage and nucleotide excision repair for larger damage like UV-induced dimers |
| base excision repair | DNA glycosylase enzyme that removes the damaged base, leaving an abasic (AP) site. then AP endonuclease cleaves the DNA backbone, then DNA polymerase fills the gap with the correct base, and finally, DNA ligase seals the nick to complete the repair. |
| nucleotide excision repair | A second complex (UvrB + UvrC) cuts the damaged strand in two places that flank the damage. This double cutting excises a short region of the damaged strand and leaves a gap that will be filled in by DNA polymerase and sealed with DNA ligase. |
| how are double stranded breaks repaired? | homologous recombination and non-homologous end joining |
| what is the methyl-directed mismatch repair in bacteria? how does it work? | it repairs almost all mistakes made by DNA polymerase; where GATC occurs, adenine methylase puts a methyl group on A. after replication, the old template bears the methyl mark, while the new daughter strand, containing the wrong nucleotides is unmarked. |
| what is the SOS system? | a bacterial DNA repair pathway that activates in response to DNA damage; Once activated, it arrests the cell cycle, initiates high-fidelity DNA repair, activate error-prone repair pathways to survive severe damage, which leads to antibiotic resistance. |
| what is the molecular basis for xeroderma pigmentosum? | a defect in DNA repair, most commonly the nucleotide excision repair (NER) pathway, caused by mutations in genes like XPA, XPC, XPD, and XPG |
| what is the molecular basis for breast cancer? | genetic mutations and epigenetic changes that disrupt cell growth and division, leading to a diverse range of subtypes |
| what is the molecular basis for the BRCA genes? | these specify proteins that function in double-strand break repair via HR. A mutation of any of these is associated with a high risk for breast cancer in females |
Created by:
angievelasco