A case study designed for a first year undergraduate genetics course. Interrmittent iClicker questions enable students to recall information from previous slides and apply it through progression of the case study. This case study was prepared as part of a pedagogical project to examine the effects of active learning versus passive learning. Animations included were independently designed using novice techniques in 3D MAX; as such they may contain inaccuracies and/or a few continuity errors.

1. LITTLE CHANGES MAKE A
BIG DIFFERENCE
The roles mutations play in genetic diseases
like cystic fibrosis

2. GENETIC LINGO – A REVIEW
• Mutation: a detectable and
heritable change in the genetic
material not caused by genetic
recombination.
• Gene: a stretch of DNA that codes
for a polypeptide or RNA.
• Alleles: are different forms
of a gene
• Genotype: represents the
genetic constitution of an
organism
• Phenotype: represents the
physical appearance of
an expressed trait

3. GENE
ALLELE
Is an alternative form
MUTATION(S)
DNA
contains
GENOTYPE
Different combinations give
affects
PROTEIN
codes for
affects
changes
PHENOTYPE
affects
Dependson
ENVIRONMENT

4. THE BUTTERFLY EFFECT OF
MUTATIONS

5. MUTATIONS: AT THE CELLULAR LEVEL
•Somatic mutations
take place in somatic
or diploid cells of the
body.
•Germ-line mutations
as the name suggests
occur within germ-line
tissue which later
develops into
gametes.

6. MUTATIONS & CYSTIC FIBROSIS
• Cystic fibrosis is an autosomal
recessive genetic disorder.
• It is caused due to a mutation in a
particular gene on chromosome 7.
• The location of this gene was
discovered in 1989 by Canadian
researcher Lap-chee Tsui at the
Hospital for Sick Kids.
• To understand a little more about
cystic fibrosis, we need to
understand what mutations are
and how minor changes in a gene
can have such drastic effects on
the overall phenotype.

7. MUTATIONS: AT THE DNA LEVEL
• Point mutations – cause the replacement of a single nucleotide with
another one.
• Frameshift mutations – these are caused by insertions or deletions of a
nucleotides which changes the open reading frame of 3 nucleotides.

8. THE DNA LEVEL
• Insertions – mutations result due to insertions of nucleotide base pairs
into DNA
• Deletions –mutations result due to deletions in DNA sequences.

9. THE SIX CLASSES OF CFTR MUTATIONS
CLASS EFFECT ON THE PROTEIN STRUCTURE/FUNCTION EXAMPLES
I Shortened protein which could result due to a
premature stop codon.
W1282X
II Failure of proteins to be delivered to the surface of
the membrane due to improper folding.
ΔF508
III The opening and closing of the CFTR channel
protein cannot be regulated.
G551D
IV Reduction in the ability of the CFTR channel protein
to conduct or transport Cl-
R117H
V Reduced quantity of functional CFTR channel
protein due to errors in RNA splicing.
3120+1G
VI* This proposed class of mutations is thought to
involve the production of functional but unstable
CFTR proteins.
Unknown

10. Discussion question
• How can a monogenic disorder like cystic fibrosis produce
so many phenotypes?

11. iClicker question
• What kind of mutation has occurred? Identify the amino acid that is missing
by using the genetic code chart on the next slide.
• A) Neutral mutation
• B) Silent mutation
• C) Frameshift mutation
• D) Transversion mutation

13. THE LOCATION OF THE MUTATION
• Around 70% of the cystic fibrosis mutations result
due to a 3-base pair deletion occurring on the
long arm of chromosome 7. This is called the
ΔF508 mutation.
• The CFTR protein is a chloride ion channel
protein that involves the transport of various ions
such as chloride ions and thiocyanate ions
among others.
• When this protein is affected, mucus, which is
normally runny becomes extremely sticky and
adheres to airways in the body.

14. STRUCTURE OF THE CFTR PROTEIN
•The CFTR protein is a
glycoprotein made up
of 1480 aminoacids.
•The protein has FIVE
domains:
1)Two membrane
spanning domains.
2)Two nucleotide binding
domains
3)A regulatory domain.
•The channel conducts
Cl- ions down their
electrochemical
gradient.

15. iClicker question
• What possible effect (s) could the ΔF508 mutation have
on the final protein structure?
• A)There is no change in the protein structure.
• B) The protein is non-functional.
• C) A protein with increased/decreased function.

16. iClicker question
• Would this mutation affect carriers equally as those
carrying two copies of the allele?
• A) No effect on both carriers and affected individuals.
• B) The mutation affects both carriers and affected
individuals.
• C) Carriers still retain some normal function due to a
normal allele being present in comparison to affected CF
individuals.

17. THE IMPACT OF THE MUTATION
• People affected by CF suffer
a myriad of problems in the
respiratory, digestive and
reproductive systems.
• The sticky mucus in respiratory
airways reduces the diameter of
respiratory airways.
• This sticky mucus blocks pancreatic
ducts and prevents the release of
digestive enzymes.
• The subsequent damage to the pancreas
affects the product of insulin – thus leading
to CFRD or cystic fibrosis related diabetes.
• Lastly the mutations in the CF gene can
cause infertility. Men are mostly affected
but women can be as well.

18. INHERITANCE
PATTERNS AND
PEDIGREES

19. PEDIGREES
• A pedigree allows geneticists
to determine the inheritance
pattern of a particular
disease.
• It can also be used to predict
the risk of having a child
with a genetic disorder.
• Probabilities are calculated
in these cases to determine
the risk of developing the
disorder.
Female Male
Unspecified sex
Affected individuals
Carriers
Diseased
Cousins
Dizygotic twins
Monozygotic twins

20. AUTOSOMAL DISEASES
• Autosomal recessive - two copies
of an abnormal gene must be
present for the disease/trait to
develop. E.g. Cystic fibrosis,
Tay Sachs
• Autosomal dominant – one copy
of the abnormal gene is required to
inherit the disease. E.g. Huntingtons
chorea, Acondroplasia

21. SEX LINKED DISEASES
• X-linked dominant - a
mutation in the X
chromosome .
E.g. Rett syndrome
• X-linked recessive –
mutation in the
X chromosome resulting in
affected males but not
females. E.g. Haemophilia
• Y-linked – a mutation in the
Y chromosome causes sons of the affected male
to be affected too. E.g.Hypertrichosis pinnae

22. iClicker question
• What mode of inheritance is this?
• A. Autosomal dominant
B. Autosomal recessive
• C. X-linked recessive
• D. X-linked dominant

23. iClicker question
• What is the mode of inheritance?
• A. Autosomal recessive
• B. Autosomal dominant
• C. X-linked recessive
• D. X-linked dominant

24. iClicker question
• Generally most genetic diseases follow Mendel’s law of
inheritance. There are exceptions to this rule however.
Examine the following pedigree:
• Talk to the person next to you to come up with a
reasonable explanation for this mode of inheritance.
Based upon your decision, would you classify this as a
germ-line or somatic mutation?*

25. HOW TO USE PROBABILITIES
SUM RULE PRODUCT RULE
PROBABILITIES
Use this if 2
independent events
occur at the same time
Use this if either of 2
mutually exclusive
events occur
Keywords: or/either Keywords: and

26. A SIMPLE EXAMPLE
• A couple are heterozygous for CF. What are the chances
of the offspring being heterozygous for the disease?
The question to be asked at this point is whether to use
the product rule or sum rule. Note that in this example, the
C allele could come from the father AND the c allele from
the mother OR C is from the mother and c from the father.
This means the probability is:
P[(C ) x (c )] + P[(C ) x (c )] = (½x ½) + (½ x ½)
= ¼ + ¼ = ½
This is thus known as the sum and product rule.

27. iClicker question
• Look at the following pedigree.
• What is the risk of having a child with cystic fibrosis?
• A) 1/64
B) 1/36
C) 1/16
D) 1/2
?

28. A CYSTIC FIBROSIS CASE
• Eva Markvoort was an ordinary
teenager from Vancouver with a
not so ordinary condition –
Cystic Fibrosis.
• For four years, she blogged about
her experiences with cystic fibrosis.
The blog was titled “65 Red Roses”.
• Sadly, she died at the age of 25 due to
her subsequent lung transplant
rejection.
• There is so far no cure for cystic
fibrosis.

29. iClicker question
• Draw out the pedigree of the Markvoort family using the
correct pedigree symbols. You already know that Eva has
cystic fibrosis. Neither her parents nor her sister have
displayed any signs of CF.
• A) B)
C) D)
?

30. iClicker question
• Based upon your pedigree, calculate the probability of
Eva’s sister being a carrier. If she has a child in the near
future, what would the probability of the child developing
CF be if:
a) Her husband is heterozygous for CF.
b) Her husband has CF. (Note: Males with CF can still
have children with assisted reproductive techniques)
• A) 7/12 and 11/24
B) 1/6 and 1/3
• C)1/2 and 3/4
• D) 1/8 and 3/8

31. SUMMARY
• Mutations in DNA can have disastrous effects on the
phenotype of the organism if allowed to persist. They can
lead to genetic diseases.
• Germ-line mutations are heritable and can manifest in a
number of phenotypes depending upon the nature of the
mutation. (E.g. Cystic Fibrosis)
• Pedigrees can be used to track the transmission of the
genetic disease through generations.
• Pedigrees can also at times be used to predict if a genetic
disorder is autosomal or sex-linked….
• …And based upon all this, a genetic counselor can
predict the probability of a couple having a child with the
same genetic disorder.

32. THE LONG ROAD AHEAD