Unit 2-Antenatal And Postnatal Screening Flashcards
What is the difference between antenatal and postnatal?
Antenatal is before birth and postnatal is after birth.
Why is antenatal care carried out?
To monitor the health of a pregnant woman and her developing foetus and baby.
What can antenatal screening identify?
The risk of a disorder so that further (diagnostic) tests can be carried out if necessary, and a parental diagnosis can be given.
What are screening tests used for?
To detect signs and symptoms associated with a condition or disorder.
Assesses risk but does not confirm.
What do screening tests require for more definite answers?
Diagnostic testing.
What is diagnostic testing?
Definite tests establishing whether a person is suffering from a specific condition or disorder.
What are the types of antenatal screening?
Ultrasound, blood and urine tests.
How many ultrasound scans is a pregnant woman given during pregnancy?
A minimum of 2.
What are the two routine ultrasound scans given during pregnancy?
A dating scan and an anomaly scan.
At what time of pregnancy is a dating scan carried out and what does this determine?
8-14 weeks.
Determines the stage of pregnancy and due date
(also use marker chemicals that vary normally during pregnancy)
At what time of pregnancy are anomaly scans carried out and what for?
18-20 weeks.
May detect any serious physical abnormalities.
Why are routine blood and urine tests carried out throughout pregnancy?
Monitor the concentrations of marker chemicals which could indicate conditions such as pre-eclampsia and Down’s syndrome.
To check the blood type of baby and woman so that Rhesus disease does not occur.
When are diagnostic tests carried out?
Routine screening has indicated a risk of a condition
or
for individuals already in high-risk categories
or
if there is a family history of a harmful genetic disorder.
What are the 2 main procedures used in diagnostic testing?
Amniocentesis
and
chorionic villus sampling (CVS).
What is the process of amniocentesis and when can it be carried out?
Carried out between 14-16 weeks.
Amniotic fluid is withdrawn which contains fetal cells.
Cultured to obtain sufficient cells to produce a karyotype for diagnosis.
What is the process of CVS and when can it be carried out?
Carried out between 9-14 weeks where a sample of placenta cells are taken from the fetal tissue.
These cells are then cultured and used for karyotyping.
What are the differences between CVS and amniocentesis?
CVS can be carried out earlier (as early as 8 weeks compared to 14-16 weeks for amniocentesis.
CVS–>placenta cells vs amniocentesis–> amniotic fluid containing fetal cells
What are risks of amniocentesis?
Miscarriage, infection, injury from the needle, inadequate results, rhesus sensitisation and club foot.
What are the risks of CVS?
Miscarriage, infection, inadequate results and rhesus sensation.
What is an advantage of using CVS rather than amniocentesis?
CVS can be carried out earlier in pregnancy than amniocentesis.
What diagnostic test carries the highest risk of miscarriage - amniocentesis or CVS?
CVS
Why are cells from CVS and amniocentesis cultured?
To obtain sufficient cells to produce a karyotype to diagnose a range of conditions.
What does a karyotype show?
The full chromosomal complement of an individual.
What is one of the first parts of postnatal screening?
Heel prick test.
Blood tested for several rare conditions including phenylketonuria (PKU).
What is phenylketonuria?
An inherited metabolic condition.
Enzyme which converts the amino acid phenylalanine to the amino acid tyrosine is non-functional. Phenylalanine severely restricts the development of the brain.
Can phenylketonuria be treated?
Treated following a low phenylalanine diet - a diet that avoids high protein foods such as eggs, meat and dairy.
Why can people with PKU still produce melanin?
They can consume tyrosine in their diet which complete the pathway to produce melanin.
What is the definition of haploid?
Only 23 chromosomes in a cell.
(Human gametes are haploid)
What is the definition of diploid?
46 chromosomes (2 sets) in a human cell (somatic cell).
What is the definition of alleles?
Different forms of the same gene.
What is the definition of dominant?
Dominant allele expressed in the phenotype over the recessive (Hh).
What is the definition of recessive?
Only expressed if both are present like (hh) not appearing with dominant.
What is the definition of homozygous?
The alleles are matching pairs HH or hh.
What is the definition of heterozygous?
The alleles are different/mixed Hh.
What is the definition of a carrier?
You have the genotype for a certain disease but it is not displayed/expressed or you do not suffer from it.
Always heterozygous Hh
What is the definition of genotype?
The genetic make up/alleles that you are actually have/are present.
What is the definition of phenotype?
The observable characteristic/trait. What you can physically see.
What is the definition of gene?
Part of your DNA/section of chromosome that codes for a protein.
In humans what are the sex chromosomes?
The X and Y chromosomes.
What are all the other chromosomes except from the sex chromosomes in the genotype called?
Autosomes.
What can be used to analyse a particular characteristic from members of a family?
A pedigree chart.
What professional would construct a pedigree chart and what would be the possible reasons for doing so?
A genetic counsellor would construct a pedigree chart when information and advice is required by a couple how are worried about passing on a genetic condition in their family to their children.
What pattern do autosomal recessive show?
- They are expressed relatively rarely.
- May skip generations.
- Males and females are affected equally.
What genotypes will suffer in an autosomal recessive inheritance trait?
Sufferers will be homozygous recessive (cc).
Non sufferers will be either homozygous dominant (CC) or heterozygous (Cc)
What pattern do autosomal dominant show?
- The trait appears in every generation.
- Each sufferer of the trait has an affected parent.
- When a branch of the family doesn’t express the trait, the trait fails to reappear in future generations of the branch.
- Males and females are affected equally.
What genotypes will suffer in a dominant recessive inheritance trait?
All sufferers are either homozygous dominant (CC) or heterozygous (Cc).
All non-sufferers are homozygous recessive.
What are disorders linked to autosomal recessive inheritance?
Cystic fibrosis.
What are disorders linked to autosomal dominant inheritance?
Huntington’s disease
What pattern do autosomal incomplete dominance show?
- The fully expressed form of the disorder occurs relative rarely.
- The partially expressed form occurs much more frequently.
- Each sufferer of the fully expressed form has 2 parents who suffer from the partially expressed form.
- Males and females are affected equally.
What genotypes will suffer in an autosomal incomplete dominance inheritance trait?
H is used to represent the normal allele, while S represents the allele for the disorder
- All sufferers of the fully expressed form of the disorder are homozygous for affected allele (SS)
- All sufferers of the partially expressed form of the disorder are heterozygous for the two alleles (HS).
- All non-sufferers are homozygous for normal allele (HH).
If an individual has the sex chromosome XX, are they male or female?
Female.
If an individual has the sex chromosome XY, are they male or female?
Male.
What is a disorder linked to autosomal incomplete dominance inheritance?
Sickle cell.
Which chromosome X or the Y, contains more genes?
The difference in size between the X chromosome and the shorter Y chromosome means some genes appear only on the X chromosome.
What are the sex-linked genes and where are they found?
The sex linked genes are the genes that are present in the X chromosome but absent in the Y chromosome.
Why is the effect of sex-linked genes more obvious in males?
A recessive allele on the X chromosome will show in the phenotype as there is no dominant allele present to override it.
What pattern do sex-linked inheritance show?
- Many more males are affected than females
- None of the sons of an affected male show the trait.
- Some of the grandsons of an affected male do show the trait.
What genotypes will suffer in a sex-linked inheritance trait?
- All sufferers of the trait are recessive (Xh Y).
- Non-sufferers of the trait are ‘homozygous’ dominant (XH Y or XH XH) or carrier females are heterozygous (XH Xh).
What is a disorder linked to sex-linked inheritance?
Haemophilia or colour blindness.
What type of inheritance may skip generations and affects females and males equally?
Autosomal recessive inheritance.
What pattern of inheritance is shown if someone can suffer a partially expressed form of a disorder?
Incomplete dominance inheritance.
In sex-linked inheritance why is the disorder seen far more often in males than in females?
The X chromosome can contain genes the Y does not
