Mutations
Mutations
• Hollywood’s images of
mutation
Mutations
• Actual Mutations
in fruit flies
What is a mutation?
• A mutation is any change in a cell’s DNA
• A mutation can occur in an individual gene
- results in a single changed protein
- cystic fibrosis a mutation in the protein that
makes a type of ion channels in cell membrane
- bacterial resistance to antibiotics is an
example of a beneficial gene mutation
What is a mutation continued
• A mutation can occur in a chromosome
- a chromosome contains many genes
- chromosomal mutations affect many
proteins
Examples: Down Syndrome
Edward’s Syndrome
Cri-du-Chat
What Causes Mutations?
• Can be caused by mutagens- a physical or
chemical cause of mutation. Examples: UV light,
radiation, drugs, and benzene.
• Mutagens are often also carcinogens – anything
that causes cancer
• Can be natural, random events.
- mutations occur in 1/100,000 DNA
replications
• Mutations do not have to be bad (evolution)
Critical Thinking
• Will all mutations have a dramatic impact on
an individual? How do you know? Which
types of mutations do you think will have the
greatest impact on an organism?
Gene Mutations
Kinds of Mutations
• Substitutions
usually affect no
more than a single
amino acid.
• Also known as
point mutations
Kinds of Mutations
The effects of insertions or deletions are more
dramatic.
The addition or deletion of a nucleotide causes a
shift in the grouping of codons.
Changes like these are called frameshift
mutations.
Kinds of Mutations
• In an insertion, an
extra base is inserted
into a base sequence.
Kinds of Mutations
• In a deletion, the loss of a single base is
deleted and the reading frame is shifted.
Knowledge Check
• What is a point mutation? Example?
• What is a frameshift mutation? Example?
Chromosomal Mutations
• Chromosomal mutations involve changes in
the number or structure of chromosomes.
• Chromosomal mutations include deletions,
duplications, inversions, and translocations.
Chromosomal Mutations
• Deletions involve the loss of all or part of a
chromosome.
Chromosomal Mutations
• Duplications produce extra copies of parts of a
chromosome.
Chromosomal Mutations
• Inversions reverse the direction of parts of
chromosomes.
Chromosomal Mutations
• Translocations occurs when part of one
chromosome breaks off and attaches to
another.
Critical Thinking
• If Down Syndrome is characterized by having 3
copies of the 21st chromosomes, would it be
explained by a gene or chromosomal
mutation? Which specific type of gene or
chromosomal mutation? Why?
Significance of Mutations
• Many mutations have little or no effect on
gene expression.
• Some mutations are the cause of genetic
disorders.
– Cancer
– Down Syndrome