b2.7 genetic disorders

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B2.7 Genetic disorders

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B2.7 Genetic disorders

B2.7 Genetic disorders

Inherited disorders: Polydactyl Cystic Fibrosis (CF) Huntington’s disease

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

Polydactyl

Polydactyl

p p

P

p

Polydactyl

p p

P Pp Pp

p pp pp

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?