Mutations
Mutation- a change in the DNA
nucleotide sequence
Mutations can be silent, cause subtle, or
dramatic effects on observed traits in
individuals
How does your DNA determine
your traits?
DNA
mRNA
protein
Observed
trait
Remember:
•Traits are determined by the functions of proteins
•Protein function is determined by protein shape
•Protein shape is determined by amino acid sequence
Mutations can change the amino
acid sequences of proteins
TACCGAGATTCA
mRNA sequence:
AU G G C U C UAAG U
amino acid sequence: Met -- Ala -- Leu -- Ser
DNA sequence:
DNA sequence:
TA T T C A
TACCGAG
AU G G C U A UAAG U
amino acid sequence: Met -- Ala -- Iso -- Ser
mRNA sequence:
How does this mutation change the
amino acid sequence?
(Original)
AAT G CATAT G CA
mRNA sequence:
UUACGUAUACGU
amino acid sequence: Leu -- Arg -- Ile -- Arg
DNA sequence:
(Mutated)
AAT T CATAT G CA
mRNA sequence:
U UAAG UAUAC G U
amino acid sequence: Leu -- Ser -- Ile -- Arg
DNA sequence:
3 types of mutations
Substitution
TA T T C A
TACCGAG
Substituting one nucleotide for another.
Insertion
TACCGA G
T ATTCA
Inserting one or more nucleotides
Deletion
TACCGA GATTCA
Deleting one or more nucleotides
Your Turn
• Complete the “Mutations practice”
worksheet. You will learn how some
mutations can affect the amino acid
sequence of proteins
• Consider how severe of an effect each
mutation would have on the ability of the
protein to function.
Question:
1. We’ve studied transcription, translation,
and replication. A mistake in which of
these processes would result in a
permanent mutation?
1. Which type of mutations had the biggest effect
on the protein sequence? WHY?
2. Which type of mutations had the smallest
effect on the protein sequence? WHY?
3. Which examples would you predict to have the
biggest effects on a trait? WHY?
4. Which examples would you predict to have the
smallest effects on a trait? WHY?
Different types of mutations happen
Substitution
TA T T C A
TACCGAG
Insertion
TACCGA G
T ATTCA
Deletion
TACCGA GATTCA
Frameshift mutations
•
•
One or more than one nucleotide can be
added or deleted with insertion and deletion
mutations.
If the number of nucleotides is not a multiple
of 3, it is called a frameshift mutation.
1. Why do we call this a frameshift mutation?
2. Can substitution mutations cause
frameshifts? Explain why or why not.
Consequences of mutations…
• If a mutation in sperm or egg DNA is not
corrected, the new sequence of DNA is
passed on to offspring.
• Over generations, more mutations
accumulate.
• As a result, differences occur between
people’s DNA sequences!
How much variation in DNA exists
between 2 people?
Hemoglobin (beta) gene sequence from person A
How much variation in DNA exists
between 2 people?
Hemoglobin (beta) gene sequence from person B
How much variation in DNA exists
between 2 people?
• About 1 in every 1,000 nucleotides is
different between 2 people
• (0.1% difference means 99.9% identical)
• We have about 3 billion nucleotides in all,
so that means there are about 3 million
nucleotide differences between 2 people
What is the observed effect of
mutations?
•
No Effect
(think about it: are there 3 million differences between 2 people?)
– Why?
1. Some mutations code for the same
amino acid
2. Most mutations are in sequences of
DNA between genes.
• Variation – there are a variety of traits in
a population.
Genetic diseases
• Many alleles are harmless, but some can
cause specific diseases.
• To determine whether a disease is genetic,
we trace the family history of a disease by
creating a type of family tree called a
pedigree.
• One disease caused by a specific
mutation is sickle cell anemia