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Flashcards in Genetics Deck (28):

Which organ do you carry out chorionic villus biopsy on?

The placenta


How could you test fetal skin cells/urine



How could you sample fetal blood?

Fetal blood sampling


When can you carry out CVS?

11.5 weeks


When can you carry out amniocentesis?

15 weeks


Earliest genetic test you can perform during pregnancy?

Fetal DNA from maternal blood (8 weeks +)
NO miscarriage risk!


Only genetic test with NO miscarriage risk

Fetal DNA from maternal blood


This test carries the risk of confined placental moscaicism

Chorionic villus biopsy


What are single nucleotide polymorphisms?

Single base changes


What are copy number variations?

Insertions or deletions of DNA segments


If you have a high risk of trisomy on screening, which test would you do next?

Array cGH


If you see a fetal abnoramlity on scanning, what test would you do next?

Array cGH


If a parent has a balanced chromosomal rearrangement, what test should you do?

Array CGH


Around what week could you see increased nuchal thickness?

Week 12


What is covered in the week 12 pre-natal screening?

This scan dates gestation and looks at the serum biochemistry
-done at week 12
-increased nuchal thickness may be seen


When is serum screening done and what does it look at?

-done week 16
-looks at maternal blood to look for biochem markers of Down syndrome


What does the 20 week detailed scan look at?

To look for other fetal abnormalities


What week could you check maternal blood for biochem markers of Down syndrome?

Week 16


What can you use non-invasive prenatal testing to look for?

-sex determination
-trisomy testing

(occasionally: chromosome deletions or looking at a single gene)

Non-invasive testing = maternal blood with fetal DNA in it)


A mother has a son with duchennes, what test can you offer?

Non-invasive prenatal testing to determine sex of the baby:
-if it is a boy do CVS (because X-linked)
-if it is a girl, reassure


Mrs Green is 12 weeks pregnant – serum biochemistry and nuchal thickness measurement gives a risk of 1 in 40 that the baby is affected with Down syndrome. What test can you do?

So she's already had the ultrasound
= do non-invasive prenatal testing
-test the mum's blood for fetal DNA


Mrs Blue comes to see you. She is 18 weeks pregnant. A detailed scan has shown that her baby has a cardiac defect: an AtrioVentricular Septal Defect that is commonly seen in Down syndrome.

Do amniocentesis and array CGH

-this is the best test for several reasons e.g. array CGH will detect small deletions such as 22q11 deletions


Trisomy 13

Patau syndrome


Patau syndrome

Tisomy 13


Bilateral cleft lip and postaxial polydactyl
Often varying degrees of holoprosencephayl sometimes resulting in cyclopia

Patau syndrome (trisomy 13)


What would array CGH look like in the parent with a balanced translocation?

aCGH would be normal (aCGH only detects imbalance)


Mrs Roberts comes to see you. She is 10 weeks pregnant. She has a balanced reciprocal translocation between chromosome 4 and chromosome 9, that has a high risk of causing a liveborn child with multiple malformations.
What tests would you do?

-chorionic villus sample
-direct karyotype/FISH may be available


When can you carry out a termination of pregnancy?

before 13 weeks = surgical
after 13 weeks = induction

There is no time limit for TOP if there is a risk of serious abnormality in the child or to the health of the mother