Genetic Screening (Edexcel A (SNAB) A Level Biology)

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Cara Head

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Cara Head

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Genetic Screening: Uses

  • Some circumstances, e.g. in a pregnancy where there is a family history of a genetic disorder, may require individuals to determine if they have a particular allele present in their genome
  • This can be determined by genetic screening
  • There are three main uses of genetic screening
    • Identifying individuals who are carrying an allele at a gene locus for a particular disorder
    • The screening of embryos prior to implantation during fertility treatment; this is Preimplantation Genetic Diagnosis (PGD)
    • Testing a foetus before birth; this is prenatal testing

Identification of carriers

  • Carrier testing is offered to individuals with a history of genetic disorders in their family
  • It can show whether people who have no symptoms carry the allele for particular disorders, such as cystic fibrosis
  • Couples can be tested prior to having children to determine the probability of future children inheriting the disorder
  • Benefits
    • Families can make informed decisions before having children
    • Women can decide whether to have prenatal testing during pregnancy

Preimplantation Genetic Diagnosis

  • IVF, or in vitro fertilisation is a type of fertility treatment during which fertilisation is carried out in the lab; embryos produced in this way can be implanted into the uterus where they develop into a foetus
  • PGD involves analysis of the DNA of an embryo prior to implanting it into the uterus
    • The sample of DNA to be analysed can be obtained by taking cell samples from embryos produced during IVF
  • Benefits
    • Reduces the chances of having a baby with a genetic disorder
    • It avoids abortion as it is carried out before implantation of the embryo

Prenatal testing

  • Prenatal testing is offered to pregnant women with a family history of genetic disorders
  • It involves testing the foetus for genetic diseases
  • The DNA can be obtained by chorionic villus sampling or amniocentesis of embryos and foetuses in the uterus
  • Chorionic villus sampling
    • This involves removing and testing a small sample of cells from the placenta using a fine needle
    • The cells contain foetal DNA which can be analysed for genetic disorders, allowing parents to make informed decisions about the pregnancy and foetus
    • It is carried out at around 11-14 weeks of pregnancy
    • The process has a  1-2 % risk of miscarriage
  • Amniocentesis
    • This involves removing and testing a small sample of cells from amniotic fluid using a fine needle
      • The amniotic fluid is the fluid that surrounds the foetus within the uterus
    • The fluid contains foetal cells which contain DNA to be analysed
    • It is carried out at around 15-20 weeks of pregnancy
    • The procedure has a 1% risk of miscarriage
  • Benefits
    • The tests allow parents to make informed decisions
    • Results can help parents prepare for the future care of the child, including medical treatment

Genetic Screening: Social & Ethical Issues

  • Genetic screening comes with a range of different social and ethical issues
  • As genetic screening can leave future parents with many questions, genetic counsellors are available to help
    • Counsellors can be seen before screening has occurred; they may discuss the following with the prospective parents
      • The probability of the couple having a child with a genetic disorder
      • Termination of the pregnancy
      • Therapeutic treatments possible for the child
      • Financial implications of having the child
      • Effect on existing siblings
      • Ethical issues
    • After screening the counsellors will read the results and explain them to the future parents
  • Each use of genetic screening brings potential concerns that should be considered
    • Identification of Carriers
      • Finding out you are a carrier can cause emotional stress and upset
      • It may impact your ability to find a partner 
      • Other genetic disorders may be identified 
      • Employers and insurance companies may use the data against an individual 
      • The tests are not always 100 % accurate; false positives or negatives may be given
    • Preimplantation Genetic Diagnosis
      • There are concerns it could lead to "designer babies" where parents select embryos with certain traits such as eye colour or sex
      • False results could lead to inaccurate information and poor decisions being made about the fate of embryos
    • Prenatal testing
      • Each procedure brings risk of miscarriage
      • False results could provide inaccurate information and poor decisions being made
      • There are ethical implications involved if parents decide to abort the fetus 

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Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding