UK GCSE level age ~14-16, ~US grades 9-10 Biology revision notes re-edit 14/05/2023 [SEARCH]

More complex genetics: 6. The genetics of Down's syndrome - genetic screening for abnormalities - ethical issues

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(6) Down's Syndrome (NOT a sex-linked inherited genetic disorder, but there is a gender link)

Down's syndrome is  genetic disorder that causes reduced muscle tone and reduced cognitive development.

 It is caused by the presence of an extra chromosome.

A sperm cell with the normal 23 chromosomes fertilises a female egg cell with 24 chromosomes.

This results in an individual with 47 chromosomes rather than the ‘normal’ 46.

An individual with the Down syndrome has three copies of the 21st chromosome rather than two.

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A note on genetic screening for genetic abnormalities

 Genetic screening involves a test for the presence of a particular allele or other genetic abnormality in the foetus.

An amniocentesis procedure is one way of performing a genetic screening test.

A needle is inserted into the amniotic fluid that surrounds the foetus in the womb and a fluid is sample is withdrawn.

Cells in the fluid from the foetus are then examined for the presence of genetic abnormalities such as Down syndrome and cystic fibrosis.

Amniocentesis does carry a 1% risk of miscarriage, and therefore usually only offered to pregnant women who are at a higher risk of having a child with a genetic abnormality.

For most mothers risk of genetic abnormalities in the bay are low, but the increases for mothers who have previously carried a foetus with a genetic abnormality, those with a family history of a genetic condition and older mothers.

Pregnant mothers can be offered a blood test between 10–14 weeks of pregnancy as alternative initial screening for Down's Syndrome, but if the blood test suggests a possibility of having a Down syndrome child, amniocentesis is normally then offered to those mothers who appear to have a higher risk.

Although not as accurate as amniocentesis, the blood test does not pose any risk to the foetus or the mother; it simply identifies those women who may wish to take the riskier amniocentesis procedure.

Whatever the method used, detection of an abnormality, poses not only potential medical problems, but ethical and moral issues including a decision to terminate a pregnancy.

Genetic screening is very controversial, for a wider discussion of its implications see ...

Genetic screening - using data from the human genome project - potential medical treatments - issues



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