antenatal and postnatal screening 2.4

Question 1

what is antenatal screening

Answer 1

antenatal (before birth) screening methods can be used to identify the risk of disorders in a fetus or embryo before it’s born

Question 2

the 2 types of ultrasound imaging

Answer 2

dating scans and anomaly scans

Question 3

dating scans

Answer 3

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

Question 4

anomaly scans

Answer 4

carries out at 18-20 weeks to detect serious physical abnormalities in the fetus

Question 5

what are biochemical tests

Answer 5

routine blood and urine tests that are carried out throughout pregnancy to monitor the concentrations of marker chemicals that vary throughout pregnancy

Question 6

what happens when marker chemicals are measured at the wrong time

Answer 6

leads to a false positive

Question 7

what happens when marker chemical concentrations are abnormal

Answer 7

lead to diagnostic testing to determine of the fetus has a medical condition

Question 8

diagnostic testing

Answer 8

carried out after a screening test to definitely establish, without doubt, whether or not the person has the condition or disorder

Question 9

what is a karyotype

Answer 9

an image of an individuals chromosomes, arranged in homologous pairs which can be used to diagnose a range of conditions

Question 10

how are karyotypes produced

Answer 10

when cells from samples are cultured to obtain sufficient cells

Question 11

amniocentesis testing

Answer 11

-small amount of amniotic fluid withdrawn which contains feral cells to produce karyotype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

Question 12

chorionic villus sampling (CVS)

Answer 12

-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

Question 13

what is PKU

Answer 13

a substitution mutation where the enzyme which converts phenylalanine to tyrosine is non functional

Question 14

what do individuals with PKU require

Answer 14

a restricted diet

Question 15

what is postnatal screening

Answer 15

health checks which are carried out after the birth of the baby

Question 16

example of postnatal screening

Answer 16

heel prick test

Question 17

what are pedigree charts used for

Answer 17

to analyse patterns of inheritance in genetic screening and counselling

Question 18

what is the info from pedigree charts used for

Answer 18

used by genetic counsellors to advise parents of the possibility of passing of a genetic condition to their child

Question 19

how many pairs of chromosomes do we have

Answer 19

23 pairs

Question 20

what are the 23rd pair of chromosomes

Answer 20

the sex chromosomes

Question 21

what are the other 22 pairs of chromosomes

Answer 21

autosomes

Question 22

autosomal recessive conditions

Answer 22

-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

Question 23

autosomal dominant inheritance

Answer 23

-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

Question 24

autosomal incomplete dominance

Answer 24

-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)

Question 25

what are sex linked genes

Answer 25

when the x chromosome is larger than the Y and carries additional genes

Question 26

why do sex linked conditions affect more males than females

Answer 26

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

Question 27

sex linked conditions

Answer 27

-sufferers are homozygous recessive (XcXc or XcY)
-non sufferers are homozygous dominant (XCXC or XCY) or heterozygous (XCXc carriers)