Exam 2 notes
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This 7 page Class Notes was uploaded by Sreya Notetaker on Monday October 12, 2015. The Class Notes belongs to BIOL 3010 at University of Toledo taught by John Gray in Summer 2015. Since its upload, it has received 30 views. For similar materials see Molecular Genetics in Biology at University of Toledo.
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Date Created: 10/12/15
Chapter 14 lecture Gene Mutation and DNA Repair 0 Darwin s concept of descent With modification 0 Many more individuals of each species are born than can possibly survive 0 Any being if it vary in any manner profitable to itself will have a better chance of survival and thus be naturally selected 0 Genetic variation is the diversity of different genomes that give rise to different individuals 0 Genomes change over time 0 Changes are heritable though the germline 0 DNA is the hereditary material I Changes in the DNA at the nucleotide level or at a higher level are the ultimate source of genetic variation 0 Recombination also gives rise to genetic variation 0 Spontaneous mutation occur in nature and mainly due to errors in DNA replication 0 Induced mutation due to chemical or physical damage 0 Categories of Mutations O Somatic not inherited most likely visible if dominant Gametic changes are heritable recessive xlinked Nutritionalbiochemical prototrophsauxotrophs Behavioral hard to discern Regulatory overunder express a gene Lethal cannot survive to reproduce Conditional ex Temperature sensitive Neutral no effect on gene product or expression 0000000 0 Molecular Basis of Mutation C THE CAT SAW TillIE Doo a Change of Loss of Gain of one letter 1 one letter one letter Substitution Deletion Insertion THE BAT SAW THE DOG THE ATS AWT HED 06 THE CMA TSA EDD G THE CAT SAW THE IHOG I T THE CAT SATIF THE DOG Loss of C Insertion of Ni Point mutation Frameshirt mutation Frameshtift mutation 2010 Pearson Education inc L L L UL L LUL L J I lllllulllv I vyluvvo pyrimidine or Purine replaces purine TEKNSW SI KSZ 8 a i ig mm ese ng by a single proton shift I Less frequent forms base pairs with noncomplementary bases 0 EX TenolGketo or Cimi Aamino If these furs epurmeynep esicpynumdane ations can occur MISSEmamage 113me haerdivehangedsteoade and gen peroxide modify bases and lead to mispairing hyd o dlfferent aa a Standard base airin arrangements NONSE N E amino acid clianged to a stop codon H CH3 039 H E N H N c C g c C Co 0 i N il c VIN EHWN C f g 1 N gc C N 1 H Thymi e kem AdEHine amino Cytosine amino Guanine keto b Anomalous basepairing arrangements CH3 O iHKIHO I H x c C I H N N ownEN HI Thymine enol Guanine Iket0 Cytosine imino Adenine amino 0 Formation of a TA to a CG transition mutation as a result of a tautomeric shift in adenine Tautomeric shift to imino form No ta utomeric shift Semiconservative replication Tautomer CA base G pair formed Anomalous 39 W i CA base pair formed 7 Tautomer N0 mutation Tautomeric 7 shift back to 9 amino form Semiconser vative v repil ication Eaiai Tiramition mutation 0 Apurinic sites and deamination spontaneous loss of purine AP site leads to inadequate template another nucleotide can be inserted 0 In domination an amino group is converted to a keto group O This causes an alteration in base pairing efficiencies 0 Induced mutations arise from DNA damage caused by chemicals and radiation 0 O 0 Base analogs chemicals that substitute for purines or pyrimindine Alkylating agents one of the first chemical mutagens known WWI Acridine dyes and frame shift mutations acridine orange can cause frame shifts they wedge between bases causing slippage or improper pairing leading to addition or deletion of a base pair 0 UV and high energy radation O O Shorter wavelength high energy UV radiation is mutagenic major effect is to induce pyrimidine dimers between adjacent base pairs along a DNA stand Ionizing radiation Xrays gamma rays cosmic rays electrons are ejected from atoms and they become free radicals leading to several types of reactions that can alter DNA 0 Single Gene Mutations casue a wide range of Human Diseases Case Studies of Mutations in Human Genes Trinucleotide repeats Huntington disease Repeat Normal Affected Number Number CAG 6 39 Organis s segl reg izgems to counteract mutations tampon rervdaystfephy gTG 535 rep 1catlon repa1 ec en mes com me nonmutated strand 1n 0 gap 0 Fraxgebles gxpi Spinolumbar Musc Dys os t a Wpolymerase SOS repair error rone because conditions are created that allow insertion of gym CGG 650 gt200 CAG 10 30 3560 Lost of CAG make Iond tracts of Chapter 6 Chromosomal mutations 0 Terminology for altered chromosomal number Terminal gf Far Variation in Chtramosome Numbers Term Explanation Aneuploidy 2H chromosomes Monosomy 2r 1 D isomy 2N Trisosmy 2 quotl Tetrasomy pentasomy etc 2n 2 2H 39 etc Ewploidy Multiples 013911 Diplloidly 2n Polyploidy 315 4H 5H Triplofidy 3n Tetraploicly pentaplaicly etc 4H 511 etc Autopollyploidy Multiples ofthe same genome Allopo lyplloid y Multiples QfleOSEly related amphidiploicly genomes 0 Examples of polyploids wheat strawberry salamanders 0 Nondisjunction causes changes in chromosome number 0 Outcome depends on when nondisjunction occurs in meiosis I or meiosis II 0 Monosomy 2nl loss of a single or part of a chromosome can have large effects 0 Down syndrome caused by an extra copy of chromosome 21 trisomy 21 O Occurs in about 1800 births O Prone to respiratory and heart malformations 0 Incidence of down s syndrome increase with maternal age 0 Few trisomies are visible in humans 0 Other than trisomy 21 only trisomy 15 patau syndrome and 18 Edwards syndrome survive to term with severe malformations and early lethality 0 Polyploidy gt2n is prevalent in plants 0 Polyploidy is where there is more than 2n chromosomes 0 Few animals lizard fish are polyploidy but not uncommon in plants 0 Tend to be even numbered 2n4n6n O Autopolploids have multiple of the same chromosomes 0 Colchicines a spindle inhibitor can induce autopolploidy in cells 0 Colchicine inhibits spindle formation causing anaphase to fails and the chromosome number doubles if the cell reenters Interphase 0 How allopolyloids form Species 1 contains genome A consisting of two distinct chromosomes ala2 and a3 Species 2 contains genome B consisting of two distinct chromosomes bl and b2 Following fertilization between members of the two species and chromosome doubling a fertile amphildiploid containing two complete diploid genomes AABB is formed 0 Deletion of part of a chromosome 0 Involves chromosome breaks and repairs a Origin of terminal deletion iA B Dr E F B E F r 7 r i 7 Break it LO cit c Formation of deficiency loop Area missing in deleted Chromosome Normal Chromosome A B E F ri J Synapsis H h J Deleted Chromosome Formation of deletion loop 0 a a terminal deletion b an intercalary deletion O c pairing occurs between a normal chromosome and one with an O intercalary deletion by looping out the undeleted portion to form a deletion loop 0 A duplication is a repeated part of a chromosome 0 O Mispairing of a tetrad during synapsis results in a deficient and duplicated chromosome The non crossover chromosomes remain unchanged 0 The role of gene duplication in evolution 0 Ohno 1970 proposed that gene duplication is essential to the origin of new genes during evolution Idea that existing genes are indispensable but by making an extra copy there is one to tinker with while original keeps on doing its job The new copy is free to accumulate mutations some of which may prove adaptive O This idea is now supported by the identification of genes with closely related sequences but different functions 0 Major jumps in evolution appear to have involved duplication of entire genomes Inversions change linear order of genes along a chromosome 0 During an inversion no information is lost usually 0 The inverted region may be short or long and may or may not include the centromere 0 If it does it is called pericentric inversion and if not then a paracentric inversion Paracentric inversion O The effects of a single crossover SCO within an inversion loop in a paracentic inversion hterozygote where two altered chromosomes are produced one acentric and one dicentric Pericentric inversion 0 The effect of a crossover in a pericentric inversion heterozygote where two altered chromosomes are produced both with duplicated and deficient regions Translocations alter the location of a chromosomal segment in the genome O Reciprocal exchange of genetic material occurs between nonhomologous chromosomes four breaks are required two on each chromosome 0 The resulting translocated chromosomes do not readily line up with the other homolog during meiosis
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