antenatal and postnatal screening 2.4 Flashcards
what is antenatal screening
antenatal (before birth) screening methods can be used to identify the risk of disorders in a fetus or embryo before it’s born
the 2 types of ultrasound imaging
dating scans and anomaly scans
dating scans
carried out at 8-14 weeks to determine the pregnancy stage and due date used with tests for marker chemicals which vary normally during pregnancy
anomaly scans
carries out at 18-20 weeks to detect serious physical abnormalities in the fetus
what are biochemical tests
routine blood and urine tests that are carried out throughout pregnancy to monitor the concentrations of marker chemicals that vary throughout pregnancy
what happens when marker chemicals are measured at the wrong time
leads to a false positive
what happens when marker chemical concentrations are abnormal
lead to diagnostic testing to determine of the fetus has a medical condition
diagnostic testing
carried out after a screening test to definitely establish, without doubt, whether or not the person has the condition or disorder
what is a karyotype
an image of an individuals chromosomes, arranged in homologous pairs which can be used to diagnose a range of conditions
how are karyotypes produced
when cells from samples are cultured to obtain sufficient cells
amniocentesis testing
-small amount of amniotic fluid withdrawn which contains feral cells to produce karyotype
-done at 15-18 weeks
-smaller risk of miscarriage than CVS but still a risk
-carried out later in pregnancy
chorionic villus sampling (CVS)
-sample of placental cells extracted to produce karyotype
-done at 11-14 weeks
-carried out earlier in pregnancy
-higher risk of miscarriage
-risks of defects of fingers and toes if carried out too early
what is PKU
a substitution mutation where the enzyme which converts phenylalanine to tyrosine is non functional
what do individuals with PKU require
a restricted diet
what is postnatal screening
health checks which are carried out after the birth of the baby
example of postnatal screening
heel prick test
what are pedigree charts used for
to analyse patterns of inheritance in genetic screening and counselling
what is the info from pedigree charts used for
used by genetic counsellors to advise parents of the possibility of passing of a genetic condition to their child
how many pairs of chromosomes do we have
23 pairs
what are the 23rd pair of chromosomes
the sex chromosomes
what are the other 22 pairs of chromosomes
autosomes
autosomal recessive conditions
-expressed rarely in offspring
-affects males and females equally
-sufferers are homozygous recessive (ff)
-non sufferers are homozygous dominant (FF) or heterozygous (Ff carriers)
-may skip a generation through carriers who don’t show the condition but can still pass it onto their offspring
-example cystic fibrosis
autosomal dominant inheritance
-expressed commonly in offspring
-affects males and females equally
-non sufferers are homozygous recessive (ff)
-sufferers are homozygous dominant (FF) or heterozygous (Ff)
-seen in every generation
-example huntingtons disease
autosomal incomplete dominance
-affects males and females equally
-non sufferers are homozygous for one incompletely dominant allele (HH)
-sufferers of the fully expressed form of the condition are homozygous for the other incompletely dominant allele (SS)
-sufferers of the partly expressed form of the condition are heterozygous (HS)
-example sickle cell trait (HS), sickle cell disease (SS)
what are sex linked genes
when the x chromosome is larger than the Y and carries additional genes
why do sex linked conditions affect more males than females
in a male (XY) each sex linked gene on the X chromosome is expressed in the phenotype as its the only form of the gene that the individual male has
sex linked conditions
-sufferers are homozygous recessive (XcXc or XcY)
-non sufferers are homozygous dominant (XCXC or XCY) or heterozygous (XCXc carriers)
