Mutations
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Mutations. Mutations. Defined : any change in an organism’s DNA Where: Single genes or entire chromosomes Some gene mutations change phenotype (physical characteristics) Example: Can cause a premature stop codon Some gene mutations don’t change phenotype.

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Mutations

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Mutations

Mutations


Mutations

Mutations

  • Defined: any change in an organism’s DNA

  • Where: Single genes or entire chromosomes

    • Some gene mutations change phenotype (physical characteristics)

      • Example: Can cause a premature stop codon

    • Some gene mutations don’t change phenotype.

      • Example: Could be silent or occur in a non-coding region

  • When: Throughout the life of the cell


Gene point mutations

Defined: one nucleotide is substituted for another

Often repaired by spellchecker enzyme

May lead to amino acid change

See animation

May not lead to any change (Silent Mutation)

Ex: DNA “CCC” is mutated into “CCG”

Same amino acid is created (glycine)

Gene: Point Mutations

T

A

C

A

G

T

G

G

T

C

A

A

A

DNA

U

G

U

C

A

C

A

C

A

G

U

U

U

mRNA

cysteine

glutamine

histidine

glutamine

phenylalanine

Amino acids


Point mutation and sickle cell disease

Point Mutation and Sickle Cell Disease

  • Hemoglobin (protein) is made from 574 amino acids

  • Sickle cell disease is caused because of 1 wrong amino acid


Gene frame shift mutation

Gene: Frame Shift Mutation

C

A

C

A

G

T

T

G

T

C

A

A

A

DNA

  • Defined: insertion/deletion of a nucleotide

  • Entire sequence of DNA/RNA after the mutation is shifted (see animation)

  • Much more serious to the structure/function of the final protein

    • mRNA sequence may have an early or late “stop codon”

G

U

G

U

C

A

A

C

A

G

U

U

U

mRNA

cysteine

glutamine

glutamine

phenylalanine

Amino acids

histidine

serine

leucine


Gene frame shift mutation1

Gene: Frame Shift Mutation

C

A

C

A

G

T

G

G

T

C

A

A

A

DNA

U

G

U

C

A

C

C

A

G

U

U

U

G

mRNA

histidine

glutamine

phenylalanine

cysteine

Amino acids

glutamine

proline

valine


Impact on offspring

Impact on Offspring

  • Somatic cell mutations

    • Affect only the individual

    • Not passed on to future generations

    • Ex: Muscle cell mutation

  • Germ cell mutations

    • Germ cells = the diploid cells that undergo meiosis to make sperm & egg

    • May be passed to future generations

If the mutated sperm above were to fertilize this egg…


Mutation causes

Mutation Causes

  • Mutagen: agents in the environment that can change DNA

    • Speed up replication process

    • Break apart nucleotides

  • Ex: UV from sunlight breaks hydrogen bond between thymine (T) and adenine (A)


  • Review

    Review

    • How are proteins affected if the DNA code is mutated?

      Example: ATTCGAGG is mutated to ATTCGTGG

    • What is the difference between a point mutation and frame shift mutations?

    • When are mutations passed on to future generations?

    • What are germs cells?

    • What is a mutagen and how do they cause problems?

    • Are all mutations considered bad/dangerous? Explain.


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