2.4- antenatal and postnatal screening

Question 1

what happens during antenatal care?

Answer 1

mothers blood pressure is monitored, blood type identified and general health checks such as blood and urine tests carried out

Question 2

what does antenatal screening do?

Answer 2

identifies the risk of a disorder so that further tests and prenatal diagnosis can be offered

Question 3

what 2 ultrasound scans are women given and when?

Answer 3

dating scan- between 8 and 14 weeks

anomaly scan- between 18 and 20 weeks

Question 4

what 2 things can a dating scan find and how?

Answer 4

determine the pregnancy stage

determine due date

use of tests for marker chemicals which normally vary during pregnancy

Question 5

what is the purpose of an anomaly scan?

Answer 5

detect serious physical abnormalities in a foetus

Question 6

why are blood and urine tests carried out during pregnancy?

Answer 6

monitor the concentrations of marker chemicals

Question 7

when do levels of HCG increase and decrease during pregnancy?

Answer 7

increase from 6-10 weeks

then decrease to a steady level

Question 8

what does it mean when HCG levels remain high after week 10 of pregnancy?

Answer 8

the foetus has downs syndrome

Question 9

when would it be meaningless to have a risk assessment and why?

Answer 9

week 10

normal and downs syndrome pregnancy would show an elevated concentration of HCG

Question 10

when would a false positive and negative occur?

Answer 10

false positive- marker chemical measured when normal value should be high

false negative- marker chemical measured when normal value should be low

Question 11

what would an atypical result in chemical concentration lead to?

Answer 11

diagnostic testing to determine if the foetus has a medical condition

Question 12

what is a diagnostic test?

Answer 12

definitive test that produces results used to establish for sure whether the person has a specific condition or disorder

Question 13

3 reasons a diagnostic test may be offered

Answer 13

evidence of a potential problem emerged from earlier routine screening tests

history of a harmful genetic disorder in her family

mother is known to belong to a high-risk category (e.g women over 35)

Question 14

2 types of diagnostic test and when they take place

Answer 14

amniocentesis- between 14 and 16 weeks

chorionic villus sampling- from 8 weeks

Question 15

what is a karyotype?

Answer 15

visual display of an individuals chromosomes arranged as homologous pairs

Question 16

how is a karyotype obtained and what is its purpose?

Answer 16

cells from samples are cultured to obtain sufficient cells

to diagnose a range of conditions

Question 17

3 steps in amniocentesis

Answer 17

a little amniotic fluid is withdrawn containing foetal cells

cells are cultured, strained and examined under microscope

full karyotype is photographed and analysed

Question 18

how long does amniocentesis take?

Answer 18

around 2 weeks

Question 19

what is the purpose of amniocentesis?

Answer 19

chromosomal abnormalities are detected

Question 20

2 advantages of amniocentesis

Answer 20

prenatal diagnosis possible

detects neural tube defect

Question 21

2 disadvantages of amniocentesis

Answer 21

small risk of miscarriage

gives results later in pregnancy

Question 22

how does chorionic villus sampling work?

Answer 22

samples of placental cells are taken using a fine tube inserted into the mothers reproductive tract

cells are cultured and used to produce a karyotype

Question 23

advantage of chorionic villus sampling

Answer 23

carried out as early as 8 weeks which allows the information to be gathered eariler

Question 24

disadvantage of chorionic villus sampling

Answer 24

has a higher incidence of miscarriages than amniocentesis

Question 25

what are the sex chromosomes in humans?

Answer 25

X and Y

23rd pair

Question 26

what are the other chromosomes in a genotype called?

Answer 26

autosomes

Question 27

what can a pedigree chart reveal?

Answer 27

pattern of inheritance

Question 28

what can be read to deduce the genotype of an individual?

Answer 28

phenotypes must be known

Question 29

who constructs a family tree and why?

Answer 29

genetic counsellor

couple requires information and advice when worried about passing a genetic disorder known to exist in their family onto their children

Question 30

what are males and females usually represented as?

Answer 30

males- squares

females- circles

Question 31

4 patterns of inheritance

Answer 31

autosomal recessive inheritance

autosomal dominant inheritance

autosomal incomplete dominance

sex-linked recessive trait

Question 32

3 characteristics of autosomal recessive inheritance

Answer 32

trait is expressed relatively rarely

trait may skip generations

males and females are affected in approximately equal numbers

Question 33

what would with and without the trait in autosomal recessive inheritance look like?

Answer 33

with the trait are homozygous recessive= cc

without the trait are homozygous dominant= CC
(OR)
without the trait are heterozygous= Cc (carrier)

Question 34

what is an example of autosomal recessive inheritance?

Answer 34

cystic fibrosis

Question 35

3 characteristics of autosomal dominant inheritance

Answer 35

trait appears in every generation

each person with the trait has an affected parent

males and females are affected approximately the same

Question 36

what would with and without the trait in autosomal dominant inheritance look like?

Answer 36

with the trait are homozygous dominant= HH
(OR)
with the trait are heterozygous= Hh (affected)

without the trait are homozygous recessive= hh

Question 37

what is an example of autosomal dominant inheritance?

Answer 37

huntingtons chorea

Question 38

when is heterozygous affected or a carrier?

Answer 38

dominant disorder allele= affected

dominant unaffected allele= carrier

Question 39

3 characteristics of autosomal incomplete dominance

Answer 39

fully expressed form of the characteristic occurs relatively rarely

partly expressed form occurs much more frequently

males and females are affected approximately the same

Question 40

what would fully, partly and without the characteristic in autosomal incomplete dominance look like?

Answer 40

with fully expressed characteristic are homozygous for one incompletely dominant allele= SS

with partly expressed characteristic are heterozygous for 2 alleles= HS

without characteristic are homozygous for other incompletely dominant allele= HH

Question 41

what is an example of autosomal incomplete dominance?

Answer 41

sickle cell anaemia

sickle cell trait

Question 42

3 characteristics of sex-linked recessive trait

Answer 42

many more males have the trait than females

none of the sons of a male with the trait show the trait

some of the grandsons of a male with the trait show the trait

Question 43

what would with and without the trait in sex-linked recessive inheritance look like?

Answer 43

with the trait are homozygous recessive= XʰY or XʰXʰ

without the trait are homozygous dominant= XᴴY or XᴴXᴴ
(OR)
without the trait are heterozygous carrier= XᴴXʰ

Question 44

what is an example of sex-linked recessive inheritance?

Answer 44

haemophilia

Question 45

what is phenylketonuria and how is it caused?

Answer 45

inborn error of metabolism

caused by a substitution mutation

Question 46

how does the substitution mutation happen in phenylketonuria?

Answer 46

protein expressed is an enzyme which should convert the amino acid phenylalanine to tyrosine but is non-functional resulting in a build up of phenylalanine

Question 47

how frequently does phenylketonuria occur?

Answer 47

1 in 10,000 in the UK

Question 48

how is phenylketonuria tested for?

Answer 48

new-borns blood is tested for excess phenylalanine within first few days of life

Question 49

what treatment is given if a baby is found to have phenylketonuria?

Answer 49

placed on a restrictive diet for life