 Cystic
Fibrosis is an inherited chronic disease
 It affects the lungs and digestive system
 Symptoms


It clogs the lungs with phlegm and causes lifethreatening infections
"obstructs the pancreas and stops natural enzymes from
helping the body break down and absorb food."
 Interesting

Facts
Cystic Fibrosis is nicknamed "65 Roses" because children
say it that way when they are diagnosed.
What Chromosome is Cystic Fibrosis Located On?
•People with cystic fibrosis
inherit a defective gene on
chromosome 7 called CFTR
(cystic fibrosis
transmembrane
conductance regulator).
•The protein produced by
this gene normally helps salt
move in and out of cells. If
the protein doesn't work,
the movement is blocked
and an abnormally thick
mucous is produced.
•The cells most seriously affected by this are the lung cells. This mucous
clogs the airways, and increases the risk of infection.



This condition is inherited
in an autosomal recessive
pattern
This means both copies of
the gene in each cell have
mutations. The parents of
an individual with an
autosomal recessive
condition each carry one
copy of the mutated gene
A person gets cystic fibrosis
when he or she inherits two
mutated CFTR genes; one
from each of their parents.
The parents don’t have it
because they have one
dominant allele that isn’t
mutated but the child
would have the two
recessive

What Are Alleles?
“Alleles are one member of a pair or
series of genes that occupy a specific
position on a specific chromosome.”
Each gene has two alleles. One from each parent.
A dominant gene is represented by a capital R.
A recessive is by a lowercase r. RR, rr, Rr
Recessive Inheritance
Both parents carry a normal gene (N), and a faulty, recessive gene (n). The parents, are
unaffected by the faulty gene. Their offspring are either affected, unaffected, or carriers.
Dominant Inheritance
One parent has a single, faulty dominant gene (D), which overpowers the normal one (d),
affecting that parent. When the affected parent mates with an unaffected and non-carrier
mate (dd), the offspring are either affected or unaffected, but they aren’t carriers.
Sex linked (x-linked) is represented with XR, or Xr, or Y. The alleles for sex-linked
traits are written as superscripts of the X or Y chromosome.

The top genotype is the father’s and the bottom is from
the mother
A
a
A AA Aa
a Aa
aa
A a
A Aa Aa
a Aa Aa
A
a Aa
Aa
a
a
aa
aa
Heterozygous dominant
Homozygous recessive
Homozygous dominant
The Punnett square shows that there is a
25% chance that a child will have the AA
genotype, a 50% chance of having the Aa
genotype and being a carrier of cystic
fibrosis, and a 25% chance of having the
aa genotype, which means that the child
will inherit the disease.

homozygous dominant: heterozygous dominant: homozygous recessive
A
a
A AA Aa
a Aa aa
o Ratios:
o1:2:1
1 (AA), 2 (Aa), 1 (aa)
oPercentages:
o 25%, 50%, 25%
25% (AA), 50% (Aa), 25% (aa)
o‘A’ represents the dominant allele
CFTR (cystic fibrosis
transmembrane conductance
regulator) and ‘a’ represents the
mutated CFTR that can cause cystic
fibrosis

A
A AA Aa
a Aa
Phenotype and Genotype
 AA: doesn’t not have cystic fibrosis (not a
carrier)



Homozygous dominant
Aa: doesn’t have the disease (carrier)

Heterozygous recessive
aa: the person has cystic fibrosis (carrier)

Homozygous recessive
a
aa
-Phenotype
- Ratios-3 will have disease: 1 wont
have disease
- Percentages-75% will have disease:
25% wont have disease
-Genotype
-Ratios-1AA:2Aa:1aa
- Percentages-25%AA:50%Aa:25%aa
A
A AA
A
AA
a Aa
Aa
A
A
A AA AA
a Aa Aa
Genotype:
Ratio:1AA:2Aa:1aa
Percentage:
25%AA:50%Aa:25%aa
Phenotype:
Ratio: 3 have
disease: 1 without the
disease
Percentage: 75%
have cystic fibrosis: 25%
don’t have the disease
- female
-male
White- person is
fine
Pink- person is
affected and has
2 “bad” genes
I
II
III
Questions:
Key
Circle: female
Square: Male
Not shaded in: person
is fine
Shaded in: person has
2 “bad” genes