Genetic screening and inheritance

• What is genetic screening 


  the analysis of DNA to see if it contains recessive, disease causing alleles
• what is identification of carriers

  - a couple without the disease is planning on having a child are tested to see if they are carriers of the diseased allele

  • this is used to check the probability of them having a child with the disorder
• what types of people is identification of carriers offered to

  - couples with a family history of the disease
• what are the advantages of identification of carriers

  - allows informed decisions to be made whether to have children or to have prenatal testing if the female is pregnant

  • allows informed decisions pre-pregnancy without the need for termination of the foetus
• what are the social and ethical issues regarding identification of carriers

  - emotional stress

  • false results may lead to incorrect decision making
  • results could be used by employers or insurance companies in a negative way resulting in discrimination
• what is PGD 


  pre implantation genetic diagnosis
• what is the process of PGD

  IVF embryonic cells DNA are analysed for the presence of disordered alleles. embryos with no disordered alleles are implanted into the womb
• what are the advantages of PGD

  1- avoids abortion

  2- reduces the risk of a child with the disease
• what are the social and ethical issues of PGD?

  embryos may be selected for certain characteristics

  embryos with the disease are discarded which could have developed into a foetus

  false results provide incorrect information
• What is prenatal testing 


  Screening fetuses for the genetic disorder offered to a pregnant female which has a family history of the genetic disorder
• at how many weeks does amniocentesis testing occur?

  15-20 weeks
• at how many weeks does CVS occur?

  11-14 weeks
• what is the advantage of CVS compared to amniocentesis 


  it is done earlier, meaning if a decision to abort is taken it is less physically traumatic, earlier results allow for more time for decision making which amniocentesis takes 2-3 weeks to get results
• what is the advantage of amniocentesis compared to CVS

  amniocentesis has a lower change of miscarriage (1% compared to 1-2%)
• how is amniocentesis carried out 


  a fine needle is inserted into the abdomen. this extracts amniotic fluids containing fetal cells, their DNA is analyzed.
• how is CVS carried out 


  a fine needs is inserted into the abdomen, or a catheter bit the vagina to extract placental cells. these cells are analyzed as they contain the same DNA as the embryo/ developing foetus
• what are the social and ethical issues regarding prenatal testing

  1- increased risk of miscarriage

  2- people believe it is unethical to abort the foetus just because it has a genetic disorder as this may lead to discrimination. furthermore the foetus potentially develops into a child.

  3- false results may lead to incorrect decisions
• What are the advantages of prenatal genetic screening? 


  Allow informed decisions on whether to terminate the pregnancy, or if the couple decides to not abort the pregnancy they have enough time to prepare for the medical treatment of their child.
• What is a mutation? 


  A random, spontaneous changes in DNA base sequence which results in an altered polypeptide chain