gene mutation


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gene mutation

  1. 1.  Discuss the difference betweenadaptation to environmental mutationsand heritable changes due to mutations List several different types of mutationsand discuss how mutations arise in cells
  2. 2.  The genetic material can be changedthrough mutations, which are changes inthe nucleotide sequences of genes Changes that are not repaired are calledmutations Early in this century, some geneticistssupported the theory that environmentalconditions could cause all heritablechanges in the genetic material(adaptations)
  3. 3.  A mutation is a change in a DNA base-pair or region of chromosome, of whichthere are many causes A somatic mutation affects the individualin which it happens and is not passed onto the succeeding generation Germ-line mutations may be transmittedby the gametes to the next generation,producing an individual with mutations inboth the somatic and germ-line cells Germ-line mutations are heritable
  4. 4.  A chromosomal mutation or aberration isa change in the structure or number ofchromosomes A gene mutation is a change in the DNAsequence of a particular gene Mutations can occur spontaneously or beinduced by a mutagen, which is achemical or physical agent that increasesthe frequency of mutational events
  5. 5.  Spontaneous mutations occur naturally A point-mutation is a base-pair substitutionmutation, in which one base pair isreplaced by another base pair (AT to GC)
  6. 6.  Point mutations include: Transition mutations, in which the change isfrom one purine-pyrimidine base pair tothe other purine-pyrimidine base pair (ATto GC, GC to AT, TA to CG, and CG to TA) Transitions can be caused byoxidative deamination.
  7. 7.  Transversion mutations involve a changefrom a purine-pyrimidine base pair to apyrimidine-purine base pair (AT to TA,GC to CG, AT to CG, and GC to TA) the consequences of this change tendto be more severe than those oftransitions. Transversions can be caused byionizing radiation.
  8. 8.  Mutations can be defined according totheir effects on amino acid sequences inproteins and include: Missense mutations, a gene mutation inwhich a change in the DNA causes achange in an mRNA codon so that adifferent amino acid is inserted into apolypeptide during biosynthesis
  9. 9.  In sickle-cell anemia: a single nucleotidebase-pair change in codon 6 of the β-hemoglobin gene leads to an amino acidsubstitution in the β-hemoglobin chain Nonsense mutations, in which an mRNAcodon is changed from an amino acid intoa stop codon (UAG, UAA, or UGA)
  10. 10. A Nonsense Mutation and its Effect on TranslationA Nonsense Mutation and its Effect on Translation
  11. 11. Types of Base-Pair Substitution MutationsTypes of Base-Pair Substitution Mutations
  12. 12.  Neutral mutations, which produce nodetectable change in the function of theprotein translated from the message It is a subset of missense mutations wherethe new codon codes for a differentamino acid which is chemically equivalentto the original one i.e Lys to Arg (proteinfunction is not affected)
  13. 13.  Silent mutations are mutations in which abase pair change transforms a codon intoanother codon for the same amino acid,with no detectable change in the resultingprotein Frameshift mutations, which result whenthe reading frame of a gene is shifted dueto the addition or deletion of one or twomore base pairs in a gene It results in a non-functional protein
  14. 14. Types of Base-Pair Substitution MutationsTypes of Base-Pair Substitution Mutations
  15. 15.  Point mutations are of two classes: Forward mutations Reverse mutations Forward mutations cause the genotype tochange from wild-type to mutant A reversion is a mutational event thatchanges a mutant phenotype back towild-type
  16. 16.  The effects of a mutation may be diminishedor abolished by a suppressor mutation(secondary or second site mutation) A suppressor mutation is a mutation at adifferent site from an original mutation thatdoes not result in a reversal of the originalmutation but instead masks or compensatesfor the effects of the initial mutation
  17. 17.  There are two major classes of suppressormutations: Intragenic suppressors occur within the samemutated genemRNA codon aaWT 5’CGT3’ CGU Arg3’GCA5’Mut 5’AGT3’ AGU Ser3’TCA5’Intragenic suppressor5’AGA3’ AGA Arg3’TCT5’ Intergenic suppressors occur in different genes
  18. 18. Mechanism of action of an intergenic nonsense suppressorMechanism of action of an intergenic nonsense suppressormutation that results from mutation of a tRNA genemutation that results from mutation of a tRNA gene
  19. 19.  Mutation rates and mutation frequencies areterms describing the quantitative measure ofthe occurrence of mutations Mutation rate presents the probability of aparticular kind of mutation as a function oftime i.e. number per nucleotide pair pergeneration or per gene per generation ex:spontaneous mutation rate in Eukaryote is10-4to 10-6per gene/generation
  20. 20.  Mutation frequency is the number ofoccurrences of a particular kind ofmutation expressed as the proportion ofcells or individuals in a population i.e. thenumber per 100,000 organisms or numberper 1 million gametes
  21. 21.  Mutations arise in DNA spontaneously as aresult of natural cellular processes Looping-out during the DNA replicationcan lead to deletion of bases on thenewly synthesized strand or on thetemplate strand. This will lead to shifted frame on the DNA. Most spontanous errors are corrected bycellular repair systems
  22. 22. Spontaneous generation of addition andSpontaneous generation of addition anddeletion mutants by DNA looping-outdeletion mutants by DNA looping-outerrors during replicationerrors during replication
  23. 23.  Mutagenic chemicals or radiation cancreate induced mutations in DNA
  24. 24.  Mutations in the genetic codeCan be induced in somatic cellsby:› Chemicals: cancerogen› Radiation: X-ray, UV› Some viruses Heredity - 5%