Mutations

Genetic Changes

What is a mutation?

A change in the base sequence of DNA

What causes mutations?

1. Mistakes in replication (spontaneous) Mistakes in base pairs

2. Environmental factors (mutagens) High energy radiation (X rays, UV rays) Chemicals (asbestos, cyanide, formaldehyde) High temperature

A mutagen

Any agent that causes a change to the DNA sequence

1. High energy mutagens (radiation) break the DNA strands apart causing deletions or substitutions

2. Highly reactive mutagens (chemical) interact with the DNA usually causing substitutions

Mutations in reproductive cells

Changes a sequence of nucleotides in a gene

May produce a new trait for the offspring

Mutations in body cells

Change in the nucleotide sequence only effects the individual and will not be passed down to the offspring i.e. Cancer, which effects genes that control

cell division in mitosis

Types of Mutations

Point mutations

Frameshift mutations

Chromosomal mutations1. Deletion

2. Insertion

3. Inversion

4. Translocation

Point mutations

A simple change in a single nucleotide base or “letter” of the gene sequence

Point mutations

1. Original:   The fat cat ate the wee rat.2. Point Mutation: The fat hat ate the wee rat

(changing the r in cat to the h in hat).

This change alters the meaning of the instructions significantly. In DNA, switching one base in the DNA sequence to a different base can change the protein that the gene makes.

Frame-shift mutations

When one or more bases are added or deleted to the DNA strand.

It shifts the reading of mRNA codons by one base

Frame-shift mutations

1. Original:   The fat cat ate the wee rat.

2. Frame Shift: The fat caa tet hew eer at.

(the “t” from cat is removed)

This type of mutation can make the DNA code meaningless and often

results in a shortened protein. 

Frame-shift mutations

Deletions

Occur when a part of the chromosome is left out. 

These can be small, such as the removal of just one "letter" or long enough to affect a large number of genes next to one another on the chromosome.

Deletions can also cause frame-shift mutations.

Deletions

1. Original:  The fat cat ate the wee rat.

2. Deletion: The fat ate the wee rat.

(deletion eliminated the word “cat.”)                                                                                         

Deletions

                                                                                        

Insertions

Result in the addition of extra DNA.

Results is duplication of genes on the same chromosome.

May also cause frame-shift mutations, and they generally result in a nonfunctional protein. 

Insertions

1. Original:  The fat cat ate the wee rat.

2. Insertion: The fat cat xlw ate the wee rat.

Inversions

An entire section of DNA is reversed.

These can be small inversions within genes or large inversions that involve large regions of a chromosome and contain several genes.

Inversions

1. Original:   The fat cat ate the wee rat.

2. Inversion: The fat eew eht eta tac rat.

Translocations

Occur when a part of one chromosome breaks off and is added to a different chromosome

Translocations

Mutation Examples