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.

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• 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