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Gene Mutations 25-4. GENETICS. Genetics is the study of the transmission of things from one generation to the next Genetic characteristics of a population can change over time “Evolution” These things can be Traits / characteristics Chromosomes Genes. GENETIC VARIATION. - PowerPoint PPT Presentation
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GENETICSGENETICSGenetics is the study of the transmission of Genetics is the study of the transmission of thingsthings from one generation to the nextfrom one generation to the next
Genetic characteristics of a population can change Genetic characteristics of a population can change over timeover time– ““Evolution”Evolution”
These These thingsthings can be can be– Traits / characteristicsTraits / characteristics– ChromosomesChromosomes– GenesGenes
GENETIC VARIATIONGENETIC VARIATIONGenetic variation is produced in two waysGenetic variation is produced in two ways
– through Mutationthrough MutationHeritable changes in DNA sequenceHeritable changes in DNA sequence
– Through Gene transferThrough Gene transferAcquiring genes from another member of our speciesAcquiring genes from another member of our species
MUTATIONMUTATIONInheritable change in DNA sequenceInheritable change in DNA sequence
Relatively rareRelatively rare
Generally occur during DNA replication or repairGenerally occur during DNA replication or repair– May also occur in response to mobile DNA May also occur in response to mobile DNA
elementselementsTransposons and virusesTransposons and viruses
May affect gene expressionMay affect gene expression
SPONTANEOUS MUTATIONSSPONTANEOUS MUTATIONSOccur without effects of outside agentsOccur without effects of outside agents
– Radiation, chemical mutagens, etc.Radiation, chemical mutagens, etc.
Various typesVarious types1.1. Base substitutionsBase substitutions
One or more base pairs changedOne or more base pairs changed
2.2. Insertions and deletionsInsertions and deletionsSometimes caused by transposable elementsSometimes caused by transposable elements– Jumping genesJumping genes
Insertion of one or more basesInsertion of one or more basesDeletion of one or more basesDeletion of one or more bases
MUTATIONSMUTATIONSPOINT MUTATIONPOINT MUTATION
One base pair alteredOne base pair alteredSubstitution can change the entire Substitution can change the entire
reading frame of the DNA causingreading frame of the DNA causing
1.1. Silent mutation – no result because same Amino Acid is Silent mutation – no result because same Amino Acid is produced (lucky there was no change)produced (lucky there was no change)
2.2. Missense mutationMissense mutationWrong AA produced which messes up the protein (Sickle Cell Anemia)Wrong AA produced which messes up the protein (Sickle Cell Anemia)
3.3. Nonsense mutationNonsense mutationStop command results, so proteins don’t even get made properlyStop command results, so proteins don’t even get made properly
SubstitutionSubstitution
Insertion MutationsInsertion Mutations
MUTATIONSMUTATIONSInsertions & Deletion MutationsInsertions & Deletion Mutations
““Frameshift mutations”Frameshift mutations”
Insertion or deletion of base pair(s)Insertion or deletion of base pair(s)– e.g., GGA e.g., GGA G GAAGA (gly GA (gly glu) glu)
Generally alter reading frameGenerally alter reading frame– ““Frameshift”Frameshift”– All downstream amino acids alteredAll downstream amino acids altered
Protein function generally affectedProtein function generally affected– Typically “knockout” mutantsTypically “knockout” mutants
Insertion / deletion & genes Insertion / deletion & genes that jumpthat jump
““Transposons” = “Jumping Genes”Transposons” = “Jumping Genes”
Transposons are DNA segments spontaneously entering Transposons are DNA segments spontaneously entering or exiting chromosomesor exiting chromosomes
Transposition into a gene constitutes a large insertionTransposition into a gene constitutes a large insertion– Gene is generally inactivatedGene is generally inactivated
Transposition out of a gene may restore gene functionTransposition out of a gene may restore gene function
TRANSPOSABLE ELEMENTSTRANSPOSABLE ELEMENTS
First discovered by Barbara McClintock in the 1940sFirst discovered by Barbara McClintock in the 1940s
Worked with maize (corn)Worked with maize (corn)
Kernel color varied as DNA sequences jumped in and Kernel color varied as DNA sequences jumped in and jumped out, messing with the pigment genesjumped out, messing with the pigment genes
no pigmentno pigment
partial pigmentpartial pigment
normal pigmentnormal pigment
TRANSPOSABLE ELEMENTSTRANSPOSABLE ELEMENTSDiscovered them in 1940s, but nobody paid attention
Ideas finally accepted in 1970s
Nobel prize in 1983 – She was 81 years old!!
Some of Barbara’s historically significant research plots were destroyed by nutcases protesting genetic engineering– None of the plants were engineered
INDUCED MUTATIONSINDUCED MUTATIONSSome mutations occur spontaneouslySome mutations occur spontaneously– RareRare
Certain chemicals or radiation can cause Certain chemicals or radiation can cause mutationsmutations– We call these “Mutagens”We call these “Mutagens”– Greatly increase the frequency of mutationsGreatly increase the frequency of mutations
e.g., 1,000X or moree.g., 1,000X or more
INDUCED MUTATIONSINDUCED MUTATIONSChemical MutagensChemical Mutagens
Chemicals Chemicals
RadiationRadiation– Ultraviolet Ultraviolet – Ionizing radiationIonizing radiation
(X-rays, gamma rays)(X-rays, gamma rays)Breaks in single strandsBreaks in single strandsBreaks in double strandsBreaks in double strandsMay result in deletions, May result in deletions, insertionsinsertions
DNA REPAIRDNA REPAIR
Mutations are rareMutations are rare– Many errors are automatically corrected by DNA Many errors are automatically corrected by DNA
Polymerase’s spell checking abilitiesPolymerase’s spell checking abilities
Mutations in genes for DNA repair enzymes are Mutations in genes for DNA repair enzymes are particularly problematicparticularly problematic– Increase mutationsIncrease mutations
NORMAL DNA REPAIRNORMAL DNA REPAIRProofreading is always happeningProofreading is always happening– DNA Polymerase detects error during synthesis DNA Polymerase detects error during synthesis – Backs up, excises wrong base, and continuesBacks up, excises wrong base, and continues– Relatively accurateRelatively accurate
Mismatch repair is completedMismatch repair is completed– Recognizes mismatch if DNA polymerase misses itRecognizes mismatch if DNA polymerase misses it– Cuts out incorrect segmentCuts out incorrect segment– Fills in gap correctlyFills in gap correctly– DNA ligase joins the segments DNA ligase joins the segments – Relatively accurateRelatively accurate