b2.7 genetic disorders
TRANSCRIPT
You are the result of two things...
and
Key words
GeneGenetic diagramsGenetic disordersInheritedDominant RecessiveAllelesPolydactylCystic fibrosis
Monohybrid crossesHomozygousHeterozygousPhenotypeGenotypeStem cellsEmbryos
Polydactyl
Polydactyly – having extra fingers or toes – is caused by a dominant allele of a gene and can therefore be passed on by only one parent who has the disorder
Cystic Fibrosis
This is a disorder of cell membranes. It is caused by a recessive allele so must be inherited from both parents. The parents may be carriers of the disorder without actually having the disorder themselves.
Cystic Fibrosis
Digestive system
Thick sticky mucus in pancreas prevents
enzyme release.Food not digested
properly.
Respiratory System
Thick sticky mucus blocks passageways in the lungs.Breathlessness and respiratory diseases.
The faulty allele is recessive (f)
An individual with one recessive allele is a carrier
An individual with two recessive alleles has cystic fibrosis
Cystic Fibrosis
F f
F
f
Cystic Fibrosis The faulty allele is recessive (f)
An individual with one recessive allele is a carrier
An individual with two recessive alleles has cystic fibrosis
F f
F FF Ff
f Ff ff
Cystic Fibrosis The faulty allele is recessive (f)
An individual with one recessive allele is a carrier
An individual with two recessive alleles has cystic fibrosis
What is the chance of two carriers having a child with CF?
F f
F FF Ff
f Ff ff
Cystic Fibrosis The faulty allele is recessive (f)
An individual with one recessive allele is a carrier
An individual with two recessive alleles has cystic fibrosis
What is the chance of two carriers having a child with CF?
F f
F FF Ff
f Ff ff
Cystic Fibrosis The faulty allele is recessive (f)
An individual with one recessive allele is a carrier
An individual with two recessive alleles has cystic fibrosis
1 in 4 or 25% or 0.25
Symptoms Loss of muscle control Forgetfulness Loss of understanding
Huntingdon’s Disease
individual with one dominant alleles has Huntington's Disease
Faulty allele is dominant
What can science do about
genetic disease?
GENETIC TESTING
• adults, fetuses or embryos• remove a cell• test for disease causing allele• adults may choose not to have children • termination of fetus with disease
PRE-IMPLANTATION GENETIC DIAGNOSIS
• fertilisation takes place in lab• remove a cell from
8 cell embryo• test for disease
causing allele• only implant embryo
without disease
GENE THERAPY• could be used to curegenetic disease eg CF• make lots of copies ofnormal allele• put alleles into virus• virus 'infects' bone marrow cells• genetically modified cells placed back inside body
CLONING
stem cellsunspecialised cells can become any type of cell
could be used to treat human illness - 'theraputic cloning'
some organisms clone themselves eg spider plants
genetically identicaldifferences caused by environment
Some of the issues...
Should we test fetuses for genetic disorders?
Are you worried about employers or insurance companies knowing your genetic information?
Is it ethical to terminate a fetus?
Is gene therapy playing God? Would you think so if it could cure you of a terminal illness?
is cloning animals acceptable?How about humans?Why? why not?