Download You and Your Genes Revision Lesson 1

You and Your
Genes
Revision Lesson 2
What causes inherited diseases?
Write:
• Huntington’s disorder and cystic fibrosis
are inherited diseases.
• They are caused by ‘faulty’ alleles of just
one gene.
Huntington’s Disorder
• Does not usually develop until over 35
years.
• Is fatal
• Symptoms: Loss of memory and mental
deterioration, loss of control over
movements.
• One faulty dominant allele (H) causes it,
so it can be inherited from just one
parent.
How is Huntington’s inherited?
Father with hh alleles
(does not have disorder)
Mother with Hh
alleles (does
have disorder)
h
h
H
Hh
Hh
h
hh
hh
There is a 50% chance that a child of these parents will inherit
the disorder.
Cystic Fibrosis
• People with cystic fibrosis produce thick,
sticky mucus.
• This mucus:
– Blocks the lungs and air passages
– Prevents enzymes getting to gut
– Encourages bacterial growth and infection
• A faulty recessive allele causes the disease
so you need 2 copies of the allele to have
it.
• A person with one faulty allele is a carrier
– They don’t have symptoms, but can pass it on
How is Cystic Fibrosis inherited?
Father with Ff alleles
(carrier of CF)
Mother with Ff
alleles (carrier of
CF)
F
f
F
FF
Ff
f
Ff
ff
There is a 25% chance that a child of these parents will inherit cystic
fibrosis.
There is a 50% chance that a child will be a carrier of cystic fibrosis.
Genetic Testing
How is genetic testing used?
• To know if a person is a carrier of a
genetic disease doctors extract genes from
white blood cells and test them for ‘faulty’
alleles.
• Cells can also be taken from young fetuses
and tested. If the test is positive, parents
may terminate the pregnancy.
• Health authorities could test a whole
population for a disease-causing allele.
This is genetic screening (expensive but
maybe cheaper than treating illness).
• Insurance companies could use genetic
testing to assess risk (not allowed in UK).
How can parents avoid having a
baby with a genetic disease?
• If one or both parents are carriers:
– In vitro fertilisation (fertilising eggs with
father’s sperm in a lab.
– Pre-implantation diagnosis (doctors test one
cell from eight-cell embryo for ‘faulty’ alleles.
– Embryo selection (doctors choose embryo
without faulty gene and implant in mother’s
uterus.
• These techniques are not always successful
Gene therapy
• Scientists think some genetic diseases can
be cured by gene therapy
• Faulty alleles are replaced with normal
alleles from healthy person.
• Has worked, but not for cystic fibrosis.
Stem Cells
• Embryos contain stem cells
• These are unspecialised cells that can
develop into any kind of cell.
• Doctors hope to use them in the future to
cure diseases.
Clones
• Some bacteria, plants and simple animals
reproduce asexually to make clones.
• Offspring have identical genes to the
parent.
• Differences are causd by environmental
factors.
• Animals do not usually form clones but:
– Identical twins are clones of each other
– Scientists have made clones
They:
– removed an egg cell nucleus
– Took another nucleus from an adult body cell
and transferred it into the ‘empty’ egg cell.
– Grew the embryo for a few days, then
implanted it into a uterus.
– Offspring born as an identical clone of ‘adult
cell’ animal.