Inherited Diseases
Cystic fibrosis
Huntington’s disease
Sickle cell anaemia
Contents
What are inherited diseases?
Haemophilia
Mutations
• Mutations may occur naturally but chances are
increased by exposure to ionising radiation and
mutagenic chemicals
• However, they can provide a source of variation
• Mutations can be are usually harmless or
deleterious
• Mutations in a gamete forming cell may be
passed on to offspring
Diseases caused by mutation
• A mutation is a change to a gene or a
chromosome
• Sickle cell anaemia is an inherited disease
caused by a mutation to a gene
• Genes are Us - Pamela's story
Sickle cell anaemia is an inherited disease that
affects red blood cells.
What is sickle cell anaemia?
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.
Normal red blood cells are shaped so that they move easily through blood vessels. This ensures that oxygen is delivered to the body.
What is sickle cell anaemia?
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
normal cells
Red blood cells normally have a lifetime of about 4 months.
What is sickle cell anaemia?
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
Sickle cell anaemia mostly affects people of African descent, but people from India, the Mediterranean and Middle East are also affected.
Who is affected by sickle cell anaemia?
It is estimated that there are around 6,000 people affected by sickle cell
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?
What alleles has a person with sickle cell anaemia inherited?
A person with sickle cell anaemia has inherited two sickle cell alleles, one from each parent.
normal allele
=
S
S
sickle cell allele
=
s
s
s
What causes sickle cell trait?
What is the genotype of a person who has inherited one sickle cell allele?
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…
S
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.
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.
Inherited Diseases
Cystic fibrosis
Huntington’s disease
Sickle cell anaemia
Contents
What are inherited diseases?
Haemophilia
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?
What is Down’s syndrome?
1 2 3 4 5
21 22 23 6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
The extra chromosome 21 in
people with Down’s syndrome leads to certain physical characteristics. However, a person with Down’s syndrome looks more like their
family than someone else with the condition. Why is this the case?
What is Down’s syndrome?
People with Down’s syndrome have various medical problems including learning difficulties and heart problems.
With the right support and medical care, they can take part in education
1 2 3 4 5
21 22 23 6 7 8 9 10
11 12 13 14 15
Down’s syndrome affects people of all ages, races, religious and economic situations.
For every 1,000 babies born, one baby will have Down’s syndrome. It is estimated that there are
around 60,000 people with
Down’s syndrome living in the UK. 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?
What causes Down’s syndrome?
1 2 3 4 5
21 22 23 6 7 8 9 10
11 12 13 14 15
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?
What has not happened when the sex cells are made to result in an extra chromosome?
The extra chromosome is introduced by mistake when sex cells are made.
The extra
What causes Down’s syndrome?
Usually, pairs of chromosomes separate when sex cells are made.
Sometimes, these pairs don’t separate properly.
If it happens that a sex cell with an extra chromosome 21
is involved in fertilization, it will lead to Down’s syndrome. This type of chromosome mutation can occur when either egg cells or sperm cells are made.
The extra
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?
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?
