Transcript 11.3 Section Summary 6.3 – pages 296

Mutations
• Any change in DNA sequence is called a mutation.
• Mutations can be caused by errors during replication,
transcription, translation, or cellular division.
Mutations that can be passed on
• Mutations HAVE to be on sex cells (gametes) in order
to be passed on to offspring.
• If a sperm or egg cell has a mutation and is fertilized,
the altered gene would become part of the genetic
makeup of the offspring.
Mutations in reproductive cells
• A mutation may produce a new trait or it may result in
a protein that does not work correctly.
• Sometimes, the mutation results in a protein that is
nonfunctional, and the embryo may not survive.
• In some rare cases a gene mutation may have
positive effects. (For instance, a mutation that caused
an owl to have bigger eyes)
• Sometimes a mutation can have no effect at all.
For instance, if a codon sequence was suppose to be
AUU
Why would it have no effect on the person if a mutation
caused the codon sequence to be
AUC
Mutations in body cells
• What happens if powerful radiation hits the DNA of a
body cell, such as in skin, muscle, or bone?
Will that affect this person’s
offspring?
• If a body cell’s DNA is changed, this mutation would
not be passed on to offspring.
• However, the mutation may cause problems for the
individual.
Types of Mutations
• A point mutation is a change in a single base pair in
DNA.
THE DOG BIT THE CAT.
THE DOG BIT THE CAR.
• Does this one letter change the meaning of the entire
sentence?
• A change in a single nitrogenous base can change
the entire structure of a protein because a change
in a single amino acid can affect the shape of the
protein.
mRNA
Normal
Protein
Stop
Replace G with A
mRNA
Point
mutation Protein
Stop
Result:
Because one base was changed from a G to an A, it caused
the wrong amino acid to be put in the protein.
• An example of a point mutation, is sickle-cell disease.
• Sickle-cell diseases cause the red blood cells to be
deformed. The result is that they get stuck in the
blood vessels, depriving tissues of oxygen, causing
strokes, and blood clots.
Types of Mutations
A point mutation takes place when a single nitrogenous
base (letter) is changed at one point.
THE DOG BIT THE CAT.
THE DOG BIT THE CAR.
What would happen if a single nitrogenous base
(letter) is deleted?
THE DOG BIT THE CAT.
THD OGB ITT HEC AT.
Is this a problem?
Types of Mutations
• A mutation in which a single base is added or deleted
from DNA is called a frameshift mutation because all
the codons shift down by one base.
Deletion of U
Types of Mutations
Result:
• Instead of just one amino acid being wrong, this
changes ALL the amino acids after the mutation.
• This causes much bigger problems than a point
mutation.
Deletion of U
Frameshift mutations
• Frameshift mutations can cause severe genetic
diseases like Cystic Fibrosis and Lou Gehrig’s
Disease.
Lou Gehrig
Stephen Hawking
• Lou Gehrig’s Disease (ALS- amyotrophic lateral
sclerosis) is a progressive neurological disease.
Affects nerve cells used for voluntary muscle control
Lou Gehrig’s Disease, or Amyotrophic Lateral Sclerosis
(ALS) is caused by a frameshift mutation on
chromosome 21.
With ALS, there is a deletion of a Cytosine on this gene.
Every other base moves down, making all the amino acids
incorrect after that.
Human Karyotype
Cystic Fibrosis
• Cystic fibrosis (CF) is one of the most common fatal
genetic disorders among Americans.
• It affects the lungs and digestive tract
NORMAL LUNG
• Due to a defective protein in the plasma membrane,
cystic fibrosis results in the formation and
accumulation of thick mucus in the lungs and digestive
tract.
Cystic Fibrosis is caused by a frameshift mutation on
chromosome 7.
Three nitrogenous bases are deleted to cause this
mutation in the amino acid sequence.
Causes of Mutations
• Many mutations are caused by factors in the
environment, such as radiation, chemicals, and even
high temperatures.
• Any external agent that can cause a change in DNA is
called a mutagen.
Repairing DNA
• Enzymes proofread the DNA and replace incorrect
nucleotides with correct nucleotides.
• These repair mechanisms work extremely
well, but they are not perfect.
• The greater the exposure to a mutagen such as UV
light, the more likely that a mistake will not be
corrected.
Question 1
Any change in DNA sequences is called a
_______.
A. replication
B. mutation
C. transcription
D. translation
The answer is B.
Question 2
Which is more serious, a point mutation or a
frameshift mutation? Why?
Answer
A frameshift mutation is more serious than a
point mutation because it disrupts more codons
than a point mutation.
Question 3
Why would a mutation on someone’s skin cell not be
passed on to their offspring?
Answer
Only mutations on gametes can be passed to
offspring.