Genetic screening and therapy

identifying carriers

prenatal testing

Preimplantation genetic diagnosis (PIGD)

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L.O 18 ­ Describe the principles of gene therapy and distinguish between somatic and germ line therapy.
Gene Line Therapy ­ involves altering the alleles inside cells to treat the cause of genetic disorders.
Carrying out gene therapy depends on whether the genetic disorder is caused by a dominant or recessive alleles:
· if caused by recessive alleles then a dominant allele can be added to make up for them
· if caused by a dominant alleles then it can be silenced by putting DNA in the middle of the allele so it doesn't work by stop ping it being used to
make protein.
CURING GENETIC DISORDERS
VIRUSES ­ the DNA sequence that allows the virus to replicate is removed and is replaced with the normal allele of the
desired gene, along with a promoter sequence that initiates transcription and translation of the gene
LIPOSOMES ­ a copy of the desired normal allele is inserted into a loop of DNA (plasmid) which are then combined with
liposomes (spherical phospholipid bilayers. The positively charged head of the phospholipids combine with the DNA (weak
acid, negatively charged) to form a liposome-DNA complex. With CF, the patient breathes in an aerosol containing these
complexes using a nebuliser then the liposomes fuse with epithelial cell membranes and carry DNA into cells.
TWO TYPES OF GENE THERAPY
SOMATIC THERAPY = involves changing the alleles in body cells particularly those affected by the disorder e.g. cystic fibrosis
is very damaging to the respiratory system so somatic therapy targets epithelial cells lining the lungs. Somatic therapy
doesn't affect the individual's sex cells so any offspring could still inherit the disease.
GERM LINE THERAPY = involves changing the alleles in the sex cells. This means that any offspring produced from these cells
will be affected by the gene therapy and won't suffer from the disease.
GERM LINE THERAPY IS CURRENTLY ILLEGAL IN HUMANS.

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GENETIC SCREENING ­ analysing DNA to identify alleles for genetic disorders
IDENTIFYING CARRIERS
Genetic screening can be performed on any DNA so it is possible to
take cheek cells, white blood cells or cells obtained from a foetus or
embryo. The DNA is tested to see whether it contains known base
sequences for the most common mutations that cause a specific
genetic disorder e.g. Cystic fibrosis.
CONNFIRMING DIAGNOSIS
Genetic screening can confirm diagnosis of genetic disorder.…read more

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L.O 19 ­ Explain the uses of genetic screening: identification of carriers using pre-implantation genetic diagnosis and
prenatal testing (amniocentesis and chronic villus sampling) and discuss the implications of prenatal genetic screening
USES OF GENETIC SCREENING
1. Carrier testing is offered to people with family history of genetic disorders
2. It helps identify whether an individual carries an allele that can cause a
genetic disorder
3.…read more

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L.O 20 ­ Identify and discuss the social and ethical issues related to genetic screening from a range of
ethical view points.
ADVANTAGES OF GENETIC SCEENING
·Early identification of treatable possible treatment for genetic disorder if parents should decide to have a child
·People can make informed decisions
· PIGD reduces the chance of having a baby with genetic disorder
·PIGD avoids the issue of abortion because only the embryo's without genetic disorders are implanted.…read more

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