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8.7 Mutations
SPONGE 6
• What do you think of when you hear the word “mutation”?
–Are they always bad?
–Give me an example
8.7 Mutations
Mutations?
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• Not all mutations are bad• Most do have negative effects
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KEY CONCEPT Mutations are changes in DNA that may or may not affect phenotype.
8.7 Mutations
• A mutation is a change in an organism’s DNA.• Many kinds of mutations can occur, especially during
replication.
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GENE MUTATIONS
1) A point mutation substitutes one nucleotide for another.
GAT CTC
GAT CAC
mutatedbase
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Example of a point mutation
• Sickle cell anemia
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2) A frameshift mutation inserts or deletes a nucleotide in the DNA sequence.
THE CAT ATE THE RAT
THC ATA TET HER AT….
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• Example of a frame shift mutation:
• Tay–Sachs disease – Develops @ around 6 months of age– Nerves start deteriorating– Child becomes blind, deaf, and unable to swallow– Death usually occurs before the 4th year
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• Chromosomal mutations – affect many genes.– may occur during crossing over
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1) Gene duplication results from unequal crossing over.
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2) Translocation results from the exchange of DNA segments between nonhomologous chromosomes.
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Mutations may or may not affect phenotype (looks).
• Chromosomal mutations tend to have a big effect. • Some gene mutations change phenotype.
– may cause a premature stop codon.– may change protein shape or the activation site.– may change gene regulation.
Ex: down syndrome
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• Some gene mutations do not affect phenotype.
– A mutation may be silent.
– A mutation may occur in a noncoding region.– A mutation may not affect protein folding or the active
site.
blockage
no blockage
Ex: Cystic Fibrosis- caused by a deletion
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• Mutations in body cells do not affect offspring.
• Mutations in sex cells can be harmful or beneficial to offspring.
• Natural selection often removes mutant alleles from a population
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Beneficial mutations CCR5 32 is a deletion thought to resist the bubonic and pneumonic plague as well as HIV
Mutations that cause resistance to antibiotics
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• Chang and Eng Bunker• Born in 1811• Married sisters• Had 21 children between
them • In modern times, they
could have easily been separated
• Died on the same day in 1874
• Chang contracted Pneumonia and died in his sleep- Eng refused to be separated from his dead twin and died several hours later.
Conjoined Twins
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Mutations caused by Mutagens
• Radiation