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DNA Mutation
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a change in the genetic material of an organism
mutations are copied during DNA replication and passed to daughter cells
mutations in reproductive cells can be passed on from one generation to another
mutations in somatic (body) cells do not affect future generations
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Causes of mutations may vary:
1. Spontaneous (randomly/by chance)
2. Sexual recombination (fertilization)
3. Gametic recombination (meiosis and cross over)
4. Environmental (chemical exposure, radiation)
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Mutagens increase the rate of changes to the DNA sequence
Physical mutagen physically change the structure of DNA (eg. xrays, UVradiation)
Chemical mutagen a molecule that induces mutations by reacting chemically with the DNA (eg. cigarette smoke)
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1. Beneficial: a mutation increases the adaptability and variation of a species (eg. Brain size in humans)
Mutation Outcomes
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2. Neutral: the mutation has no effect due to a change in the:
a) nonsense strand this gene is not transcribed nor translated b) intron: the gene is transcribed but not translated (spliced out) c) mRNA: mutation is transcribed but results in a codon for the same amino acid
Mutation Outcomes
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3. Deleterious: gene change manifests disease/death (eg.,cystic fibrosis, hemophilia, muscular dystrophy, dyslexia)
Mutation Outcomes
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Classes of Mutations
1. Silent: not expressed
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Classes of Mutations
1. Silent: not expressed
occurs in nonsense strand or intron region
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Classes of Mutations
1. Silent: not expressed
transcription and translation of the sense strand still results in a healthy protein
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Classes of Mutations
2. Nonsense: is expressed
changes a healthy codon into a deleterious one, usually lethal
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Classes of Mutations
2. Nonsense: is expressed
often changes an amino acid codon to a stop codon eg. UAT → UAG
transcription ceases and translation does not occur, no protein is produced
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Classes of Mutations
3. Missense: is expressed
causes a shift in the reading frame (eg. point, deletion, insertion, inversion mutations)
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Classes of Mutations
3. Missense: is expressed
changes the amino acid sequence, producing a new/foreign protein transcription and translation still occur
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Mutations Impact Different Levels
Single gene/point mutation (can be missense, nonsense or silent)
involves a single nitrogenous base
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Mutations Impact Different Levels
3 types of point mutations:
1) addition/insertion AGC GAA → AGU CGA A
Ser Glu → Ser Arg
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Mutations Impact Different Levels
3 types of point mutations:
2. Subtraction/deletion
GCA AGC UGA → GAA GCU GA Ala Ser Stop → Glu Ala
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Mutations Impact Different Levels
3 types of point mutations:
3. Substitution : wobble effect (possibly)
AGC GAA → AGU GAA Ser Glu → Ser Glu
AGC GAA → AGG GAA Ser Glu → Arg Glu
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Mutations Impact Different Levels
Multigene mutations
involves blocks of genes called “transposons”
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Mutations Impact Different Levels
Multigene mutations
1. Deletions or duplications
portion of chromosome is deleted or duplicated
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Mutations Impact Different Levels
Multigene mutations
2. Translocations
involves large segments at the chromosome level
a relocation of groups of base pairs from one part of the genome to another
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Mutations Impact Different Levels
Multigene mutations
2. Translocations
the DNA sequences that "swapped" places are called transposons
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Mutations Impact Different Levels
3. Inversions chromosome segments reverse orientation
no gain or loss of genetic material
involves homologous chromosomes
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