Genetics Flashcards
what procedure needs to be done to sample the DNA in the placenta?
chorionic villus biopsy
amniocentesis tests DNA in what cells?
baby’s skin and urine cells
what procedure is done to assess fetal blood?
fetal blood sampling
when is amniocentesis done?
15 weeks and over
a chorionic villus biopsy is done at what gestation?
11.5 weeks
name 3 genetic analyses that can test the whole genome of the fetus?
array CGH
whole genome sequencing
fetal DNA from maternal serum
name 3 genetic analyses that test targeted areas of the fetal genome?
point mutation testing
FISH
quantitive fluorescent PCR
difference between mutation and polymorphism?
polymorphisms dont necessarily cause disease
what is a copy number variation?
insertions or deletions of DNA segments
if you suspect an abnormality that is too small to be seen on a whole chromosome, what test should you do?
FISH
if you suspect an abnormality that is big enough to be seen on a whole chromosome, what test should you do?
array CGH
when would you do karyotyping over array CGH?
high risk of trisomy
fetal abnormality on screening
parent has balanced chromosomal rearrangement
when is the first dating USS done?
12 weeks
at what gestation is serum screening done?
16 weeks gestation
what is being tested in non-invasive prenatal testing (NIPT)?
maternal blood (contains fetal blood)
main indication for NIPT?
- suspected aneuploidy (extra/missing chromosome) eg trisomies
2, fetal sexing
genetic Ix for duchenne MD?
chorionic villus sample
what congenital heart defect is commonly seen in downs syndrome?
atrioventricular septal defect
what genetic test is best when unsure of the genetic cause?
array CGH
what is better: an unbalanced chromosome rearrangement or sex chromosome aneuploidy?
sex chromosome aneuploidy eg X inactivation
define a robertsonian translocation
two acrocentric chromosomes stuck end to end
you are at increased risk of what if you have a robertsonian translocation?
trisomy
what would aCGH look like in someone with a balanced translocation?
normal
only detects imbalance
unbalanced translocations have what consequences for the fetus?
if large, miscarriage
if small, dysmorphic delayed child
name the different genetic tests from most general to most specific
chromosome analysis
aCGH
PCR and sanger sequencing
NGS
how specific is NIPT?
very specific down to 1 base pair
what does “c.” stand for in a genetic sequence
the position in the mRNA that the mutation is
what does “c.267 + 2T>A” mean in terms of mutation location
267 codons in, at the 2nd base in the codon there is a substitution from T (normal) to A (the mutation)
> means what in genetics?
substitution eg C>G
when can cardiac abnormalities be spotted on USS?
12-20 weeks
when can short limbs be detected on USS?
after 22 weeks
“banana shaped cerebellum”…
spina bifida
a suspected chromosome abnormality would prompt what investigations?
array cGH
how can you sex a fetus without invasion?
test mums blood for Y chromosomes
risk of X linked disease if baby is male?
1 in 2
risk of X linked disease in children?
1 in 4
how is DNA tested in pregnancy?
PCR
how is DNA sampled in pregnancy
chorionic villus biopsy at 11.5 weeks
amnio at 16+ weeks
Ix patient with duchenne MD who wants to see if their baby has duchenne?
sexing on fetal DNA then proceed to either CVB or amnio depending on estation
risk to all couples of a congenital problem is 1 in __
200
_% of embryos have an abnormal chromosome makeup
50
how is fertilisation done in preimplantation genetic testing?
ICSI
when is an embyro biopsied for PGD? how many cells is it made of?
8 cells at day 3 post fertilisation
sex determination is done by what process in PGD?
FISH
when would you consider PGD?
paremtal chromosomal abnormality
x linked disorder
single gene disorders eg CF
