Unit 2 KA4 - ante and postnatal screening Flashcards
techniques an be carried out to monitor the health of the …….., ………… and …………
mother, developing fetus, and baby
what is the meaning and purpose of antenatal screeening?
screening before birth to identify the risk of a disorder so further tests and a prenatal diagnosis can be offered
give examples of antenatal screening
ultrasound imaging, blood and urine tests and diagnostic tests
what is ultrasound imaging?
when an ultrasound scanner is held against pregnant women’s abdomen and picks up high frequency sounds that have bounced off the fetus
these are converted to an ultrasound image on a computer screen
what are the 2 types of ultrasound screening and when are they carried out?
dating scan - 8-14 weeks
anomaly scan - 18-20 weeks
why is the dating scan carried out?
to determine the stage of pregnancy and due date
used alongside tests for marker chemicals
why is the anomaly scan carried out?
detects presence of serious physical abnormalities in the fetus e.g. spina bifida
when and why are blood and urine tests carried out?
throughout pregnancy to monitor concentration of marker chemicals
atypical chemical concentrations indicate a ……., so ………… ………… must take place
problem, diagnostic testing
what leads to a false-positive result in a blood/urine test?
measuring a chemical at the wrong time since marker chemicals vary at different stages of pregnancy
what is diagnostic testing?
definitive test that produces results used to establish if the fetus is suffering a specific condition/disorder
in which cases is diagnostic testing offered to a pregnant woman?
- screening tests have shown a potential problem
- family history of genetic disorders
- she belongs to a high-risk group (e.g women over the age of 35)
give examples of diagnostic testing?
amniocentesis and chorionic villus sampling (CVS)
what is a karyotype and where are they produced from?
shows an individual’s chromosomes arranged as homologous pairs
produced from fetal cells which have been cultured
what are karyotypes used for?
to diagnose a range of conditions
where are fetal cells obtained from?
amniocentesis and CVS
when is amnio and CVS carried out?
amnio - 14-16 weeks
CVS - 8 weeks
describe the process of amniocentesis
amniotic fluid containing fetal cells are withdrawn
they are cultured, stained, and examined under a microscope to create the karyotype
give an advantage and disadvantage of amniocentesis
advantage - chromosome abnormalities can be detected
disadvantage - risk of miscarriage
describe the process of CVS
a tiny sample of placental cells are taken using a fine tube inserted into the mother’s reproductive tract
the cells are cultured and used for karyotyping
give an advantage and disadvantage of CVS
advantage - can be carried out at 8 weeks whereas amnio is 14-16 weeks
disadvantage - higher risk of miscarriage than amnio
a family tree looking at ………………. is constructed by a ……………
analysis to spot …….. and ……… chances of parents producing offspring with …………..
genetic conditions/disorders, genetic counsellor, patterns, predict, genetic disease
once …….. of family members are known, the …….. can be worked out
phenotypes, genotypes
X and Y chromosomes are called………. and all other chromosomes are called……..
sex chromosomes, autosomes
give an example of autosomal recessive inheritance
cystic fibrosis
what patterns can be spotted by a geneticist in autosomal recessive inheritance?
- the trait is expressed rarely
- the trait may skip generations
- the trait is expressed in some of the offspring of a consanguineous marriage
- males and females are affected in approx. equal numbers
what are the genotypes of sufferers and non-sufferers in autosomal recessive inheritance?
sufferers - homozygous recessive (ff)
non-sufferes - homozygous dominant (FF) or heterozygous (Ff)
give an example of autosomal dominant inheritance
huntington’s disease
what patterns can be spotted by a geneticist in autosomal dominant inheritance?
- the trait is expressed in every generation
- each sufferer of the trait has an affected parent
- males and females are affected in approx. equal numbers
what are the genotypes of sufferers and non-sufferers in autosomal dominant inheritance?
non-sufferers - homozygous recessive (hh)
sufferers - homozygous dominant (HH) or heterozygous (Hh)
give an example of autosomal incomplete inheritance
sickle cell disease
what patterns can be spotted by a geneticist in autosomal incomplete inheritance?
- the fully expressed form occurs rarely
- partly expressed form occurs more frequently
- each sufferer of the fully expressed form has 2 parents who suffer from the partly expressed form
- males and females are affected in approx. equal numbers
what are the genotypes of sufferers (partly expressed and fully expressed) and non-sufferers in autosomal incomplete inheritance?
sufferers (fully expressed) - homozygous for the other incompletely dominant alleles (SS)
sufferers (partly expressed) - heterozygous for the two alleles (HS)
non-sufferers - homozygous for one incompletely dominant allele (HH)
give an example of sex-linked recessive traits
hemophilia
what patterns can be spotted by a geneticist in sex-linked recessive traits?
- more males than females are affected
- none of the sons of an affected male show the trait
- some grandsons of an affected male show the trait
what are the genotypes of sufferers and non-sufferers for sex-linked recessive traits?
sufferers are homozygous recessive
non-sufferers are homozygous dominant
why and why is postnatal screening carried out?
after birth when the baby is a few days old to test for metabolic disorders
what is phenylketonuria (PKU) caused by?
a subsitution mutation which distrupts the metabolic pathway that converts phenylalanine into tyrosine a the enzymes that catalyses this conversion is non functioning
how are newborn babies screened for PKU and what steps are taken if they are a sufferer?
by having their blood tested for the presence of excess phenylalanine
PKU sufferers are put on a restricted diet to limit amount of phenylalanine
