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Genetics Chapter 13
Gene mutations, transposable elements, and DNA repair
| Term | Definition |
|---|---|
| mutations | inherited change in the DNA sequence |
| what are the two broad categories of mutations? | somatic mutations and germline mutations |
| somatic mutations | arise in somatic tissues, which do not produce gametes |
| germ-line mutations | arise in cells that ultimately produce gametes |
| somatic mutations: when a somatic cell with a mutation divides (mitosis_, the mutation is passed on to the daughter cells, leading to what> | a population of genetically identical cells (a clone) |
| somatic mutations: cells with somatic mutation that stimulates cell division can increase in number and spread. This type of mutation can give rise to cells with a selective advantage and is the basis for ______ | cancers |
| germ-line mutations: can be passed to future generations, producing what? | individual organisms that carry the mutation in all their somatic and germ-line cells |
| germ-line mutations: chromosome mutations refers to what? | large-scale genetic alteration that affects chromosome structure or the number of chromosomes |
| germ-line mutations: gene mutations refers to what? | changes in a single gene |
| gene mutations: what are the three basic types of gene mutations? | substitutions, insertions, and deletions |
| gene mutations: base substitution | alteration of a single nucleotide in the DNA |
| gene mutations: there are two types of base substitutions... | transition and transversion |
| gene mutations: transition | purine replaced by purine or pyrimidine replaced by pyrimidine (substitution of like bases) |
| gene mutations: transversion | purine replaced by a pyrimidine or vice versa (substitution of unlike bases) |
| gene mutations: the number of possible transversions is _____ the number of possible transitions, but _________ arise more frequently | twice, transitions |
| gene mutations: insertion | nucleotides are added |
| gene mutations: deletion | nucleotides are removed |
| gene mutations: frameshift mutations | insertion or deletion that alters the reading frame of a gene |
| gene mutations: in-frame deletion or insertion | deletion or insertion of a multiple of three nucleotides that does not alter the reading frame |
| gene mutations: expanding nucleotide repeats | regions of DNA that consist of repeated copies of sets of nucleotides |
| gene mutations: increased numbers of nucleotide repeats are associated with what? | several genetic disorders |
| gene mutations: forward mutation | changes wild-type phenotype to a mutant phenotype |
| gene mutations: reverse mutation | changes a mutant phenotype back to the wild-type phenotype |
| gene mutations: missense mutation | changes a sense codon into a DIFFERENT sense codon |
| gene mutations: what do missense mutations result in? | the incorporation of a different amino acid in the protein |
| gene mutations: nonsense mutation | changes a sense codon into a NONSENSE codon |
| gene mutations: what do nonsense mutations cause? | premature termination of translation |
| gene mutations: silent mutation | changes a sense codon into a SYNONYMOUS codon, leaving the amino acid sequence of the protein unchanged. |
| gene mutations: neutral mutation | changes the amino acid sequence of a protein without altering its ability to function |
| gene mutations: loss-of-function mutation causes what? | complete or partial loss of function |
| gene mutations: gain-of-function mutation causes what? | produces entirely new trait or causes a trait to appear in a n inappropriate tissue or at an inappropriate time |
| gene mutations: conditional mutations | expressed only under certain conditions |
| gene mutations: lethal mutations | causes premature death |
| gene mutations: suppressor mutation | suppresses the effect of an earlier mutation at a different site |
| gene mutations: intragenic suppressor mutation | suppresses the effect of an earlier mutation within the SAME gene |
| gene mutations: intergenic suppressor mutation | suppresses the effect of an earlier mutation within a DIFFERENT gene |
| concept check: how does a suppressor mutation differ from a reverse mutation? | reverse mutation restores the original phenotype by changing the DNA sequence back to wildtype. a suppressor mutation restore the phenotype by by causing an additional change in the DNA at a site different from the original mutation |
| frequency with which a wildtype allele at a locus changes into a mutant allele is referred to as the _________ _______ | mutation rate |
| mutation rates are generally low and are affected by ________ and _________ factors | environmental and genetic |
| mutations that occur under normal conditions are called ____________ mutations | spontaneous |
| mutations that result from changes caused by the environmental chemicals or radiation are _______ mutations | induced |
| tautomeric shifts occur when ________ of protons in the DNA bases change | positions |
| mispairing can also occur through wobble. explain | normal, protonate, and other forms of the bases are able to pair because of the flexibility in the DNA helical structure |
| when a mismatched base has been incorporated into a newly synthesized nucleotide chain, an ___________ error is said to have occurred | incorporated |
| an example of incorporated error: T (normally pairs with A) mispairs with G through wobble. The next round of replication, what will happen? | the two mismatched bases separate, and each serves as template for the synthesis of new nucleotide strand. T pairs with A producing copy of original DNA. G pairs with C, producing new DNA with C-G pair in place of T-A pair |
| the original incorporated error leads to a _________ error which creates a PERMANENT mutation because all the base pairing are correct and there is no mechanism for repair systems to detect the error | replicated |
| insertions and deletions can be caused by what two things? | strand slippage and unequal crossing over |
| strand slippage | occurs when one nucleotide strand forms a small loop. |
| strand slippage: if the looped-out nucleotides are on the NEWLY synthesized strand, what occurs? | an insertion (insertion will be replicated and both strands will contain an insertion) |
| strand slippage: if the looped-out nucleotides are on the TEMPLATE strand, what occurs? | a deletion (will be perpetuated in subsequent rounds of repliction) |
| unequal crossing over: in normal crossing over, homologous sequences of the two DNA molecules align, and crossing over produces no net change in the number of nucleotides in either molecule. __________ pairing can cause unequal crossing over | misaligned |
| unequal crossing over results in what? | one DNA molecule with an insertion and the other with a deletion |
| spontaneous chemical changes: depurination | the loss of a purine base from a nucleotide |
| spontaneous chemical changes: depurination results when... | the covalent bond connecting the purine to the 1'-carbon atom of the deoxyribose sugar breaks |
| spontaneous chemical changes: deamination | the loss of an amino group (NH2) from a base |
| spontaneous chemical changes: the deamination of cytosine produces ________ | uracil |
| depurination and demination can alter the __________ properties of the bases and cause errors in subsequent rounds of replication | pairing |
| chemically induced mutations: any environmental agent that significantly increases the rate of mutation above the spontaneous rate is called a ________ | mutagen |
| chemically induced mutations: one class of chemical mutagen consist of base analogs, which are what? | chemicals with structures similar to that of any of the four standard bases of DNA |
| chemically induced mutations: bases analogs are inserted into DNA and frequently pair with the wrong ____ | base |
| chemically induced mutations: alkylating agents, deaminating chemicals, hydroxylamine, and other chemicals do what? | change the structure of DNA bases, altering their pairing properties |
| chemically induced mutations: intercalating agents do what? | wedge between the bases and cause single-base insertions and deletions in replication |
| ionizing radiation such as X-rays and gamma rays damage DNA how? | by dislodging electrons from atoms |
| What do these electrons then do? | they break phosphodieter bonds and alter the structure of bases |
| UV light causes mutations primarily by producing _________ ______ that disrupt replication and transcription | pyrimidine dimers |
| bacteria can sometimes circumvent replication blocks produced by pyrimidine dimers and other types of DNA damage by means of the ___ system | SOS |
| the SOS system enables bacteria to what? | overcome replication blocks (but introduces mistakes in replication) |
| Bruce Ames developed a simple test for evaluating the potential of chemicals to cause cancer. The ames test is based on the principle that... | both cancer and mutations result from damage to DNA |
| the Ames test uses ___ strains of bacteria to test chemicals for their ability to produce ___--->___ mutations | his- strains. his- ---> his+ mutations |
| any chemical that significantly increases number of colonies appearing on the treatment plate is mutagenic and therefor probably also c___________ | carginogenic |
| transposable elements | mobile DNA sequences that often cause mutaitons |
| when staggered cuts are made in the target DNA, transposable element inserts itself into the DNA. The staggered cuts leave shor, single-stranded pieces of DNA. replication of this single-stranded DNA creates what? | flanking direct repeats |
| flanking direct repeats | short (3-12 bp) directly repeated sequence produced on either side of a transposable element |
| at the ends of many, but not all transposable elements are _________ ______ ______ | sequences from 9 to 40 bp that are inverted complements of one terminal inverted repeats |
| terminal inverted repeats | sequences from 9 to 40 bp that are inverted complements of one another |
| _____________ is the movement of a transposable element from one location to another | transposition |
| several different mechanisms are used for transposition, but all types have 3 things in common | (1) staggered breaks are made in the target DNA (2) transposable element is joined to single-stranded ends of target DNA (3) DNA is replicated at the single-strand gaps |
| some transposable elements transpose as DNA (instead of first being copied into RNA) and are referred to as ___ _________ | DNA transposons |
| other transposable elements transpose through an RNA __________ | intermediate |
| transposition through RNA intermediate: RNA is transcribed from the transposable element (DNA) and is then copied back into DNA by a special enzyme called ______ _________ | reverse transcriptase |
| elements that transpose through an RNA intermediate are called _____________ | retrotransposon |
| DNA transposons: replicative transposition | a new copy of the transposable element inserts in a new location and the old copy stays behind |
| DNA transposons: nonreplicative transposition | the old copy excises from the old site and moves to a new site |
| transposons are _______ and have played an important role in genome evolution | mutagenic |
| increases in copy number of transposable elements have contributed to what? | the large size of may eukaryotic genomes |
| a number of pathways exist for DNA repair. Most require two nucleotide strands because why? | a template strand is needed to specify the correct base sequence |
| DNA repair: mismatch repair | corrects incorrectly inserted nucleotides that arise in the course of replication |
| DNA repair: incorrectly paired bases are detected and corrected by mismatch-repair ______ | enzymes |
| DNA repair: how do the mismatch-repair enzymes do this? | it cuts out distorted section and fills gap with new nucleotide by using the original DNA strand as a template |
| DNA repair: another type of DNA repair is _______ ________, which changes altered nucleotides back into their original (correct) structures | direct repair |
| DNA repair: ____-______ repair, a modified base is first excised and then the entire nucleotide is replaced | base-excision repair |
| DNA repair: the excision of modified bases is catalyzed by a set of enzymes called DNA _________, each of which recognizes and removes a specific type of modified base | glycosylases |
| DNA repair: in _________-_______ repair, bulky DNA lesions that distort the double helix are removed | nucleotide-excision repair |
| defects in DNA repair are the underlying cause of several genetic diseases. Many of these diseases are characterized by a predisposition to ______ | cancer |
Created by:
cmccartney2