Download KS4 Inherited diseases

Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What are inherited characteristics?
Each person inherits characteristics
from their parents.
How are inherited characteristics
passed on from one generation
to the next?
Inherited characteristics are passed
on in the chromosomes inherited
from your parents.
Each chromosome contains genes
that code for characteristics such as
eye colour, hair type and height.
Can a disease also be an inherited
characteristic?
What is an inherited disease?
Genes pass on characteristics
from one generation to the next.
Each chromosome contains
hundreds of different genes.
A mutation in just one gene
can change a characteristic.
Sometimes this change has
a harmful effect on the body
and can lead to disease.
This type of condition is called
an inherited disease.
Is an inherited disease contagious?
Examples of inherited diseases
What causes an inherited disease?
Each matching pair of chromosomes contains
one chromosome inherited from each parent.
gene for a
characteristic
chromosome from
female parent
matching
gene
chromosome from
male parent
Each pair of chromosomes contains the same type
of genes that code for the same characteristics.
What are different versions of a gene called?
What causes an inherited disease?
Different versions of a gene, that code for different
versions of a characteristic, are called alleles.
gene for a
characteristic
matching
gene
normal
allele
disease
allele
For some genes, there is an allele that can cause disease.
Does inheriting an allele that causes disease always lead
to the development of that disease?
What causes an inherited disease?
The development of an inherited disease depends
on the combination of alleles that a person has inherited.
gene for a
characteristic
matching
gene
normal
allele
disease
allele
Inherited diseases, like other inherited characteristics,
can be caused by dominant or recessive alleles.
What is the difference between dominant and recessive
alleles?
What causes an inherited disease?
If an inherited disease is caused by a dominant allele,
how many alleles will cause the disease to develop?
disease
allele
1 dominant disease allele
(from either parent)
normal
allele
inherited
=
disease
Does it matter which parent a dominant disease allele
is inherited from?
What causes an inherited disease?
If an inherited disease is caused by a recessive allele,
how many alleles will cause the disease to develop?
disease
allele
disease
allele
2 recessive disease alleles
inherited
=
(one from each parent)
disease
Are inherited diseases always passed on?
The inheritance of an inherited disease depends on
two main factors:
 the genes carried by the parents;
 the particular sex cells that combine during fertilization.
How can you work out the chance that genes for inherited
disease will be passed on to the next generation?
A genetic cross can be used to determine the possible
offspring and the likelihood that genes are passed on.
Understanding inherited diseases
Why is it useful to be able to predict the probability of
inherited disease?
It’s useful for people who know that there is a history of
inherited disease in their family.
Being able to make predictions about genetic disease,
they can work out what might happen if they have children.
People often need advice about such an important issue.
This is called genetic counselling.
Genetic counsellors can help people discuss any concerns
they might have and help them make informed decisions
for themselves.
What information would a genetic counsellor need
to know about a couple seeking their advice?
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What is cystic fibrosis?
Cystic fibrosis is an inherited
disease that affects many
body organs, particularly the
lungs and digestive system.
The air passages in the lungs
are coated with a constant flow
of mucus, which traps and
removes bacteria.
In a person with cystic fibrosis,
mucus is thicker than normal.
This thick, sticky mucus can block
the lungs and airways. How will this
affect a person with cystic fibrosis?
What is cystic fibrosis?
A person with cystic fibrosis
has breathing difficulties.
They are at risk of repeated
chest infections which can
lead to lung damage.
People with cystic fibrosis
need daily physiotherapy,
which involves massage to
help loosen the sticky mucus.
Antibiotics help to treat and
control lung infections and
prevent lung damage.
What is cystic fibrosis?
Treatment for the cystic fibrosis
also includes special inhalants.
In severe cases, a lung transplant
operation is required.
The thick, sticky mucus that
affects the lungs of a person
with cystic fibrosis can also
affect their digestive system.
What problems might this cause?
People with cystic fibrosis can
have problems digesting food.
Most take enzyme pills when
they eat to supply missing
enzymes and allow digestion.
Living with cystic fibrosis
Over 7,500 people in the UK
are affected by cystic fibrosis.
The quality of life for people
with cystic fibrosis is much
better than in earlier times,
due to improved treatment
and understanding of this
inherited disease.
Children born with cystic
fibrosis do not have a normal
life expectancy, although this
is improving all the time.
How is cystic fibrosis inherited?
Cystic fibrosis is caused by a recessive allele.
What symbols could stand for the different forms of this gene?
c =
C =
cystic fibrosis allele
normal allele
What alleles has a person with cystic fibrosis inherited?
c c
A person with cystic fibrosis has the genotype cc.
They have inherited a cystic fibrosis gene from both parents.
How is cystic fibrosis inherited?
How do you represent the genotype of a person
who inherits one cystic fibrosis allele?
C c
Does a person with this genotype have cystic fibrosis?
A heterozygous person (Cc) is called a carrier.
They do not have the disease but they do carry the cystic
fibrosis allele which they might pass on to their children.
In the UK, 2.3 million people carry the cystic fibrosis gene.
If both parents are carriers of the faulty gene, what is the
chance that their children will have cystic fibrosis?
Cystic fibrosis inheritance activity 1
Cystic fibrosis inheritance activity 2
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What is sickle cell anaemia?
Sickle cell anaemia is an
inherited disease that
affects red blood cells.
Normal red blood cells
contain haemoglobin,
a protein that carries
oxygen around the body.
In sickle cell anaemia,
red blood cells have
abnormal haemoglobin.
This distorts red blood
cells to form curved,
sickle shapes.
How will sickle cells affect the bloodstream and the body?
What is sickle cell anaemia?
Normal red blood cells are
shaped so that they move
easily through blood vessels.
This ensures that oxygen is
delivered to the body.
normal cells
move freely
Sickle-shaped red blood cells
can get stuck in narrow blood
vessels and cause blockages.
Oxygen is prevented from
getting to the body’s tissues
and organs. This leads to
severe pain and can cause
permanent organ damage.
sickle cells
get stuck
What is sickle cell anaemia?
Red blood cells normally have
a lifetime of about 4 months.
Sickle cells are fragile and
only last for 10–20 days.
How will this affect the level
of red blood cells?
The shorter lifetime of sickle cells reduces the number of
red blood cells leading to anaemia.
People with anaemia feel weak and tired.
Children with sickle cell anaemia are able to lead normal
lives but need regular medical attention. Treatment
sometimes includes blood transfusions.
Who is affected by sickle cell anaemia?
It is estimated that there
are around 6,000 people
affected by sickle cell
disorders in Britain.
Sickle cell anaemia mostly
affects people of African
descent, but people from
India, the Mediterranean
and Middle East are also
affected.
What causes sickle cell anaemia?
Sickle cell anaemia is caused by a recessive allele.
What symbols could stand for the different forms of this gene?
s =
sickle cell allele
S =
normal allele
What alleles has a person with sickle cell anaemia inherited?
s s
A person with sickle cell anaemia has inherited two sickle
cell alleles, one from each parent.
What causes sickle cell trait?
What the genotype of a person who has inherited
one sickle cell allele?
S s
Does a person with this genotype have sickle cell anaemia?
The sickle cell allele is recessive so this person does not
have the disease. They are a carrier of the sickle cell allele
and have what is called sickle cell trait.
People with sickle cell trait must avoid becoming dehydrated
and short of oxygen.
But having sickle cell trait isn’t all bad news…
Sickle cell trait and malaria resistance
Carriers of the sickle cell
allele (Ss) are more
resistant to malaria.
Malaria is a serious disease
caused by parasites.
It is spread by bites from
infected mosquitoes.
Malaria parasites enter red
blood cells. The effects
include fever and vomiting
and can be fatal.
Why is the sickle cell allele common in areas of the world
where malaria is or has been widespread?
Sickle cell trait and malaria resistance
The sickle cell allele may be
due to a genetic mutation that
occurred in malaria-prone
areas many years ago.
People with sickle cell trait
were more likely to survive a
malaria outbreak and live long
enough to have children, so
the trait might be passed on.
The disadvantage of the sickle cell allele is the possibility
that children may be born with sickle cell anaemia.
If both parents are sickle cell carriers, what is the chance
that their children have sickle cell anaemia?
Sickle cell anaemia inheritance activity
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What is Huntington’s disease?
Huntington’s disease is an inherited
disease that affects the brain and
central nervous system.
The wide-ranging symptoms of this
inherited condition usually develop
in adults between the ages of 30 and 50 .
Huntington’s disease causes damage
to nerve cells in the areas of the brain
involved in the control of movement,
planning and motivation.
How will this affect a person with
Huntington’s disease?
What is Huntington’s disease?
People with Huntington’s disease are
affected by gradual physical, mental
and emotional changes.
The early symptoms of Huntington’s
disease include:
 mild tremor
 clumsiness
 lack of concentration
 problems remembering things
 depression
 mood changes, sometimes including aggressive behaviour.
People can have symptoms for several years before
finding out they have Huntington’s disease.
Why can it take so long for this disease to be diagnosed?
What is Huntington’s disease?
The physical, mental and emotional
symptoms of Huntington’s disease
become progressively worse.
As the disease continues, people may
experience involuntary movements,
weight loss, speech problems and
extensive memory loss. Eventually
a person with Huntington’s disease
needs complete nursing care.
Currently there is no cure for Huntington’s disease.
Medication is available to help treat some symptoms such
as involuntary movements, depression and mood swings.
Around 4 800 people in the UK have Huntington’s disease.
How is Huntington’s disease inherited?
Huntington’s disease is caused by a dominant allele.
What symbols could stand for the different forms of this gene?
H =
Huntington’s allele
h =
normal allele
If someone inherits one Huntington’s disease allele will they
develop the disease?
H h
The Huntington’s disease allele is dominant, so inheriting
one allele from either parent will lead to this condition.
How is Huntington’s disease inherited?
Huntington’s disease is caused by a
dominant allele and can be passed on
by one parent who has the disease.
Anyone who inherits the Huntington’s
allele will develop the disease, usually
between the ages of 30 and 50.
People with the Huntington’s allele may have had a family
before realizing that they have inherited the disease.
If one parent has the Huntington’s allele and the other is a
non-carrier, what is the chance that their children will have
Huntington’s disease?
Huntington’s disease inheritance activity
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What is haemophilia?
Haemophilia is an inherited disease
in which blood cannot clot properly.
A person with this condition is
called a haemophiliac.
They do not produce the clotting
factor needed for the blood to clot
and so bleed for longer than normal.
Cuts and grazes are not a major problem – a little pressure
and a plaster are usually enough to stop bleeding.
Internal bleeding is a much more serious problem
affecting joints, muscles and soft tissue.
What is haemophilia?
Treatment for haemophilia usually
involves injections to replace the
missing clotting factor.
Haemophiliacs can be treated on
a regular basis to prevent bleeding
or when bleeding occurs.
About 6 000 people in the UK are affected by haemophilia.
Most of these are males, while females are carriers of this
condition.
Haemophilia is called a sex-linked characteristic.
Which chromosomes do you think are involved in the
inheritance of this blood disorder?
How is haemophilia inherited?
Haemophilia is caused by a recessive allele on the
X chromosome (one of the sex chromosomes in pair 23).
X chromosome
haemophilia
allele
Y chromosome
no gene to match
haemophilia allele
The other sex chromosome, the Y chromosome, is much
shorter than the X chromosome.
It does not carry a gene to match the haemophilia allele.
Why is haemophilia known as a sex-linked condition?
How is haemophilia inherited?
Haemophilia is caused by a recessive allele carried
on the X chromosome.
What symbols could stand for the different forms
of the X chromosome?
h
haemophilia allele
on X chromosome
H
normal allele
on X chromosome
X =
X
=
Why does inheritance of the haemophilia allele affect
males and females differently?
Haemophilia in females
What happens if a female inherits one haemophilia allele?
H
h
X X =
female
carrier
The recessive haemophilia allele is masked by the
dominant normal allele on the other Y chromosome,
so the woman is not affected by the disease.
Why is this type of female called a carrier?
Haemophilia in females is an extremely rare condition.
This occurs if the woman inherits two haemophilia alleles.
h
X X
h
=
female with
haemophilia
Haemophilia in males
What happens if a male inherits one haemophilia allele?
h
X Y =
male with
haemophilia
If a man inherits one haemophilia allele, he will be affected
by haemophilia.
The haemophilia allele is normally recessive but in this case
the Y chromosome does not carry a matching allele that
might mask the disease.
The inheritance of one haemophilia allele is enough for a
man to be affected by the disease.
Which parent will have passed on the haemophilia allele?
Haemophilia genotypes
© Boardworks Ltd 2004
Haemophilia – the royal disease
In about one third of all cases of haemophilia there is no
family history of the disease.
The condition is caused by a spontaneous mutation
in the person with haemophilia or their mother.
The most famous example of such a case
was Queen Victoria. None of her ancestors
had haemophilia but her son, Leopold,
was born with the condition.
Two of Victoria’s daughters were carriers.
They married into European royal families
and haemophilia was called the royal disease.
What is the chance that a carrier woman and an unaffected
man will have a son with haemophilia?
Haemophilia inheritance activity 1
Haemophilia inheritance activity 2
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
What is Down’s syndrome?
Down’s syndrome is an inherited
condition that results in
characteristic physical features
and various medical problems.
It is not a disease or illness.
A person with Down’s syndrome
has an extra chromosome
in their body cells.
This additional chromosome is an
extra copy of chromosome 21.
What is the total number of
chromosomes in the body cells
of a person with Down’s syndrome?
1
2
3
4
5
6
7
8
9
10
11
12
13 14 15
16
17 18
19 20
21
22 23
What is Down’s syndrome?
The extra chromosome 21 in
people with Down’s syndrome leads
to certain physical characteristics.
1
However, a person with Down’s
syndrome looks more like their
6
family than someone else with the
condition. Why is this the case?
11
People with Down’s syndrome
have various medical problems
16
including learning difficulties
and heart problems.
With the right support and medical
care, they can take part in education
and have full and varied lives.
2
3
4
5
7
8
9
10
12
13 14 15
17 18
19 20
21
22 23
What causes Down’s syndrome?
Down’s syndrome affects people
of all ages, races, religious and
economic situations.
For every 1,000 babies born,
1 baby will have Down’s syndrome.
It is estimated that there are
around 60,000 people with
Down’s syndrome living in the UK.
1
2
3
4
5
6
7
8
9
10
11
12
13 14 15
16
Nothing done before or during
pregnancy can cause Down’s
syndrome. It can happen to anyone.
So where does the extra
chromosome 21 come from?
17 18
19 20
21
22 23
What causes Down’s syndrome?
The extra chromosome 21 can come from either parent
and is present at fertilization.
Which type of cells will the extra chromosome be found in?
The extra
chromosome
can be in an
egg cell or
sperm cell.
The extra chromosome is introduced by mistake when
sex cells are made.
What has not happened when the sex cells are made
to result in an extra chromosome?
What causes Down’s syndrome?
Usually, pairs of chromosomes separate when sex cells
are made.
Sometimes, these pairs don’t separate properly.
The extra
chromosome
can be in an
egg cell or
sperm cell.
This type of chromosome mutation can occur when either
egg cells or sperm cells are made.
If it happens that a sex cell with an extra chromosome 21
is involved in fertilization, it will lead to Down’s syndrome.
What causes Down’s syndrome?
For example, a woman might produce an egg cell
in which chromosome pair 21 have not separated.
How many chromosomes will the egg cell contain?
24 chromosomes
+
+
23 chromosomes
If this egg is fertilized by a normal sperm cell, how many
chromosomes will a baby with Down’s syndrome have in
each body cell?
47 chromosomes
Contents
Inherited Diseases
What are inherited diseases?
Cystic fibrosis
Sickle cell anaemia
Huntington’s disease
Haemophilia
Down’s syndrome
Summary quiz
Multiple-choice quiz