8.7 – Mutations. Key Concept Mutations are changes in DNA that may or may not affect phenotype....
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Transcript of 8.7 – Mutations. Key Concept Mutations are changes in DNA that may or may not affect phenotype....
![Page 1: 8.7 – Mutations. Key Concept Mutations are changes in DNA that may or may not affect phenotype. mutated base.](https://reader035.fdocuments.us/reader035/viewer/2022062321/56649eb35503460f94bbb575/html5/thumbnails/1.jpg)
8.7 – Mutations8.7 – Mutations
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Key ConceptMutations are changes in DNA that may or may
not affect phenotype.
mutatedbase
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What Are Mutations?What Are Mutations?
Changes in the nucleotide sequence of DNA
May occur in somatic cells (aren’t passed to offspring)
May occur in gametes (eggs & sperm) and be passed to offspring
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Are Mutations Helpful or Harmful?
Mutations happen regularly
Almost all mutations are neutral
Chemicals & UV radiation cause mutationsMutagens are anything in the environment that can cause mutations
Many mutations are repaired by enzymes
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Are Mutations Helpful or Harmful?
Some types of skin cancers and leukemia result from somatic mutations
Some mutations may improve an organism’s survival (beneficial)
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Types of Mutations
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Chromosome Mutations
May Involve:Changing the structure of a chromosome
Loss or gain of part of the chromosome
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Chromosome Mutations
Five types exist:DeletionInversionTranslocationNondisjunctionDuplication
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Deletion
Due to breakage
A piece of a chromosome is lost
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Inversion
Chromosome segment breaks off
Segment flips around backwards
Segment reattaches
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Duplication
Occurs when a gene sequence is repeated
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TranslocationInvolves two chromosomes that aren‘t homologous
Part of one chromosome is transferred to another chromosome
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Nondisjunction
Failure of chromosomes to separate during meiosis
Causes gamete to have too many or too few chromosomes
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NondisjunctionCan cause “Trisomy” (three copies of
the same chromosome in an egg or sperm)Trisomy 21 (Down syndrome)
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Chromosome Mutation Animation
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Gene MutationsChange in the nucleotide sequence of a gene
May only involve a single nucleotide
May be due to copying errors, chemicals, viruses, etc.
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Types of Gene Mutations
Include:Point MutationsSubstitutionsInsertionsDeletionsInversionsFrameshift
Similar to the chromosomal versions of these mutations
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Point Mutation
Change of a single nucleotide
Includes the deletion, insertion, or substitution of ONE nucleotide in a gene
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Point Mutation
Sickle Cell disease is the result of one nucleotide substitution
Occurs in the hemoglobin gene
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Nonsense MutationType of point mutation
Results in a premature stop codon and usually a nonfunctional protein
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Frameshift Mutation
Inserting or deleting one or more nucleotides
Changes the “reading frame” like changing a sentence
Proteins built incorrectly
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Frameshift Mutation
Original:The fat cat ate the wee rat.
Frame Shift (“a” added): The fat caa tat eth ewe era t.
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Amino Acid Sequence Changed
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Gene Mutation Animation
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Silent Mutations
Some mutations have no effect and are called “silent”Example:GUC changed to
GUGBoth code for the
amino acidvaline
This would not affect the proteinbeing made in any way
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Mutations may or may not affect phenotype.Chromosomal mutations tend to have a big
effect.
Some gene mutations change phenotype by:causing a premature stop codon.causing a change in protein shape or the active
site.causing a change in gene regulation.
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Some gene mutations do not affect phenotype.
A mutation may be silent because….
– It occurs in a non-coding region.
– It may not affect protein folding or the active site.