How fast do you think DNA Polymerase can add
nitrogen bases (A, T, G, or C) during DNA
Replication (in base pairs per minute)?
DNA Polymerase can replicate DNA at a rate of
50,000 base pairs per minute!
That’s pretty fast – do you
think it ever makes
mistakes?
Mutations
Mutations
• Changes in the genetic code
• They come from mistakes that cells have made in
copying their own DNA.
– If a cell has a mutation, all of its daughter cells will inherit
the same mutation!
How many cells have the mutation?
A.
B.
C.
D.
1
6
7
8
7!
Types of Mutations
• Gene Mutation: produces a change in a single gene
• Chromosomal Mutations: produce changes in whole
chromosomes & affect many genes
– Can change the locations of genes on chromosomes!
Gene Mutations
• Point Mutation: involve changes in 1 or a few
nucleotides at 1 point in the DNA sequence
– Substitutions
– Frameshift Mutations
THE DOG BIT THE CAT
Point
Mutation
THE DOG BIT THE CAR
Point Mutations – Substitutions
• 1 base is changed into another
– Usually affect only 1 amino acid
Point Mutations – Substitutions
Point Mutations – Frameshift Mutations
• Insertions or Deletions: an extra base is added or removed
– These usually affect a large part of the protein!
Remember!
Bases are read in groups of 3, but
if 1 base is added or removed,
this shifts the “reading frame” of
the genetic code & can change all
amino acids after the site of the
mutation!
Deletion
The original: THE DOG BIT THE CAT
Deletion: THE DOG BIT HEC AT
Insertion
The original: THE DOG BIT THE CAT
Insertion: THE DOE GBI TTH ECA T
Point Mutations – Frameshift Mutations
Chromosomal Mutations - Inversion
• Reverses the direction of parts of the chromosomes
Chromosomal Mutations - Translocation
• Part of 1 chromosome breaks off & attaches to
another
Chromosomal Mutations – Deletions &
Duplications
• Deletion: part of the chromosome is lost
• Duplication: there is an extra copy of part of the
chromosome
What type of chromosome mutation does
Brenden have?
A.
B.
C.
D.
Inversion
Translocation
Deletion
Duplication
Inversion!
Effects of Mutations
• An amino acid may or
may not change!
– For example, the codons
GCC & GCA both code for
the same amino acid,
alanine!
– However, mutating AGC
to AGA will change the
amino acid from serine to
arginine!
All mutations are
harmful.
A. True
B. False
False!
Effects of Mutations
• Any new trait in a population, good or bad, is a result
of a mutation!
• Neutral: no effect on protein function
• Harmful: cause genetic diseases
• Beneficial: gives the organism a better chance of
survival
Examples
• Neutral: Blue eyes was caused by a mutation that first
appeared 6-10 thousand years ago!
• Harmful: An albino person has a frameshift mutation in
melanin producing genes. Albinism makes organisms more
susceptible to skin cancer.
• Beneficial: Mutations in the CCR5 gene in humans makes
them almost immune to HIV!
Which type of mutations are more likely to be
harmful?
A.
B.
C.
D.
E.
Substitutions
Insertions
Deletions
A&C
B&C
Insertions & Deletions! These mutations will always cause a
frameshift mutation, which will change the reading frame & the
amino acid sequence! This will give you a completely different
protein!
Substitutions could change the amino acid sequence, but it may
not.
Exit Ticket – Before you leave, answer the
following question on a sheet of paper (share!):
The majority of plants & animals are able to make
their own Vitamin C. Some animals, including
humans, guinea pigs, & some birds, have lost their
ability to make Vitamin C due to a mutation. Would
you consider this mutation to be harmful, neutral, or
beneficial? Why?