Genetic Screening
2.15 i) Understand the uses of genetic screening, including the identification of carriers, pre-implantation
genetic diagnosis (PGD) and prenatal testing, including amniocentesis and chorionic villus sampling.
ii) Understand the implications of prenatal genetic screening.
2.16 Be able to identify and discuss the social and ethical issues related to genetic screening from a range
of ethical viewpoints.
Genetic Testing
• Sometimes called genomic testing.
• Finds changes in genes that can cause health problems.
• Mainly used to diagnose rare and inherited health conditions and some cancers.
To Identify Carriers
• Genetic testing can identify carriers, allowing parents to make informed decisions.
For Testing Embryos
• Prenatal genetic testing (testing of DNA from an embryo/fetus).
• Third technique in early stages of development.
Prenatal Testing
• Involves screening unborn babies (foetuses) for genetic disorders.
• Two types: amniocentesis and chronic villus sampling.
Amniocentesis
• Carried out 15-17 weeks of pregnancy.
• Sample of amniotic fluid (that surrounds the fetus) is obtained via the abdomen using a fine needle.
• Fluid contains fetus cells, which can be analysed.
• Advantages:
o 1% risk of miscarriage (lower than CVS).
o Rapid tests (which only look for the most common disorders) can also be performed, with results
available within 3-4 days.
• Disadvantages:
o Regular results aren’t available until 2-3 weeks after the sample is taken.
o Invasive technique.
o Takes place later in the pregnancy than chronic villus sampling.
Chronic Villus Sampling
• Carried out 8-12 weeks of pregnancy
• Tests placental tissue removed through the wall of the abdomen or vagina.
• Advantages:
o Placental tissue provides more DNA than amniotic fluid
o Takes placer earlier in the pregnancy than amniocentesis.
o Initial results (which tell you whether any obvious major issues have been found) are available in a
few days.
• Disadvantages:
o Invasive technique.
o 1-2% risk of miscarriage (greater than amniocentesis).
o The results of more in-depth and detailed tests can take two or more weeks.
32
2.15 i) Understand the uses of genetic screening, including the identification of carriers, pre-implantation
genetic diagnosis (PGD) and prenatal testing, including amniocentesis and chorionic villus sampling.
ii) Understand the implications of prenatal genetic screening.
2.16 Be able to identify and discuss the social and ethical issues related to genetic screening from a range
of ethical viewpoints.
Genetic Testing
• Sometimes called genomic testing.
• Finds changes in genes that can cause health problems.
• Mainly used to diagnose rare and inherited health conditions and some cancers.
To Identify Carriers
• Genetic testing can identify carriers, allowing parents to make informed decisions.
For Testing Embryos
• Prenatal genetic testing (testing of DNA from an embryo/fetus).
• Third technique in early stages of development.
Prenatal Testing
• Involves screening unborn babies (foetuses) for genetic disorders.
• Two types: amniocentesis and chronic villus sampling.
Amniocentesis
• Carried out 15-17 weeks of pregnancy.
• Sample of amniotic fluid (that surrounds the fetus) is obtained via the abdomen using a fine needle.
• Fluid contains fetus cells, which can be analysed.
• Advantages:
o 1% risk of miscarriage (lower than CVS).
o Rapid tests (which only look for the most common disorders) can also be performed, with results
available within 3-4 days.
• Disadvantages:
o Regular results aren’t available until 2-3 weeks after the sample is taken.
o Invasive technique.
o Takes place later in the pregnancy than chronic villus sampling.
Chronic Villus Sampling
• Carried out 8-12 weeks of pregnancy
• Tests placental tissue removed through the wall of the abdomen or vagina.
• Advantages:
o Placental tissue provides more DNA than amniotic fluid
o Takes placer earlier in the pregnancy than amniocentesis.
o Initial results (which tell you whether any obvious major issues have been found) are available in a
few days.
• Disadvantages:
o Invasive technique.
o 1-2% risk of miscarriage (greater than amniocentesis).
o The results of more in-depth and detailed tests can take two or more weeks.
32
