Mutations

What’s the deal with these organisms?

What is a Mutation?

• A Mutation is any change in the nitrogen base sequence (order) in DNA

How can a change in DNA of a gene effect the protein product?

• Remember… • A change in DNA (mutation) will lead to a change in the mRNA

• A change in mRNA can lead to a change in the protein made

• The protein might not work as well, or might not work at all!

Types of Mutations – Point Mutations

• Point mutations occur when there is a change in a single (1) nucleotide of a DNA sequence

• Types of point mutations

– Substitution

– Addition

– Deletion

Point Mutation - Substitution

• A substitution mutation occurs when one base is changed to a different base

Insertion Mutation

• An insertion mutation is when a base is inserted, or added to the DNA sequence

• Insertion mutations are also called frameshift mutations because they shift the reading frame of the sequence

Deletion Mutation

• Deletion mutations are when a base is removed from the DNA sequence

• Deletion mutations are also frameshift mutations

Chromosomal Mutations

• Chromosomal mutations are when the number or structure of chromosomes change

– These include deletions, duplications, inversions, and translocations

Deletion

• Deletion involves the loss of all or part of a chromosome

• Gene “B” is missing

Duplication

• Duplication produces and extra copy of all or part of a chromosome (2 copies of “B”)

Inversion

• Inversion reverses the direction of parts of a chromosome (B and C switched)

Translocation

• Translocation occurs when part of one chromosome breaks off and attaches to another

Mutagens

• A mutagen is a chemical or physical agent in the environment that can cause a mutation

– Some chemical mutagens include

• Pesticides

• Tobacco smoke

• Environmental pollutants

– Some physical mutagens include

• X-rays

• Ultraviolet light

Effect of mutations on genes

• Mutations can have several different types of effects on genes

– Some have little or no effect

– Some can cause beneficial variation

– Some negatively disrupt gene function

• The change in DNA can change the mRNA, which can lead do different amino acids in protein!

Types of mutations

• A mutation that has no effect on the protein that a gene produces is called a silent mutation

• A mutation that changes one amino acid in the sequence in a protein is called a missense mutation

• A mutation that causes a premature, or early, stop signal (and a significantly shortened protein) is called a nonsense mutation

Harmful Mutations • If a mutation dramatically changes the protein

structure or activity negatively, the mutation is considered harmful

• A protein that doesn’t function properly usually leads to problems in the organisms

• One example of a harmful mutation is the mutation that causes sickle cell disease – A protein in the red blood cell doesn’t function

correctly, and the shape of the blood cell changes as a result

Sickle Cell Disease

Beneficial Effects

• If a mutation produces proteins with new or altered functions that can be useful to organisms in different or changing environments, that mutation is considered beneficial

• Example, mutations have helped many insects resist certain chemical pesticides