2.4

Question 1

What is the goal of antenatal screening?

Answer 1

aims to detect abnormalities in the foetus and pregnancy and assess risk of developing certain disorders.

Question 2

What is the role of a dating scan?

Answer 2

to determine the stage of the pregnancy and to estimate the due date. Tests for chemical markers of pregnancy are also perfomed at the dating scan.

Question 3

What is the role of an anomaly scan?

Answer 3

to detect potential serious physical abnormalities in the foetus.

Question 4

Why are blood and urine tests carried out throughout pregnancy?

Answer 4

to monitor the concentrations of pregnancy marker chemicals.

Question 5

What is amniocentesis?

Answer 5

an antenatal screening technique which involves collecting a sample of amniotic flud from the amniotic sac for analysis of genetic disorders.

Question 6

What are the advantages of amniocentesis?

Answer 6

• prenatal diagnosis possible
• detects neural tube defect

Question 7

What are the disadvantages of amniocentesis?

Answer 7

• small risk of a miscarriage
• gives results later in the pregnancy

Question 8

What is chorionic villus sampling (CVS)?

Answer 8

an antenatal screening procedure that involves collecting a sample of cells from the placenta for analysis of genetic disorders.

Question 9

What is an advantage of CVS?

Answer 9

it can be carried out as early as 8 weeks and therefore allowing the information to gathered earlier

Question 10

What is an disadvantage of CVS?

Answer 10

CVS causes a higher incidence of miscarriage than amniocentesis.

Question 11

Give three difference between amniocentesis and CVS

Answer 11

1. amniocentesis is carried out between 14-16 weeks, whereas CVS can be performed at 8 weeks.
2. amniocentesis involves collecting amniotic fluid, whereas CVS involves collecting cells from the placenta.
3. the results from amniocentesis take a couple of weeks to come back, however CVS allows for immediate karyotyping.

Question 12

What is the main risk involved in performing amniocentesis and CVS?

Answer 12

there is a risk of miscarriage for both amniocentesis and CVS risk is slightly higher in CVS.

Question 13

What is involved in genetic counselling?

Answer 13

involves investigating, discussing and treating possible genetically-linked medical conditions that may affect an individual or their famiy.

Question 14

What is a dominant allele?

Answer 14

produces its associated phenotype whether its paired allele is the same or different.

Question 15

What is a recessive allele?

Answer 15

produces its associated phenotype only when its paired with the same recessive allele.

Question 16

Describe the term “homozygous”

Answer 16

a cell that has inherited two identical alleles of the same gene

Question 17

Describe the term “heterozygous”

Answer 17

a cell that has inherited two different alleles of the same gene

Question 18

Describe what happens in incomplete dominance inheritance patterns

Answer 18

This occurs when neither allele is dominant over the other for a gene. When both appear in the genotype, the phenotype is a mixed picture of the two.

Question 19

What is an example of autosomal incomplete dominance?

Answer 19

Sickle cell anaemia (fully expressed) and sickle-cell trait (partly expressed)

Question 20

What are the characteristics associated with autosomal incomplete dominance?

Answer 20

• the fully expressed form of the charcateristic occurs relatively rarely
• the partly expressed form occurs much more frequently
• males and females are affected in approximately equal numbers

Question 21

What is the genotype of the fully expressed form (sickle-cell anaemia) of the characteristics - autosomal incomplete dominance

Answer 21

homozygous for the other incomplete dominant allele
SS

Question 22

What is the genotype of the partly expressed form (sickle-cell trait) of the charcteristics - autosomal incomplete dominance

Answer 22

heterozygous for the two alleles
HS

Question 23

What is the genotype of someone without the characteristics - autosomal incomplete dominance

Answer 23

homozygous for one incomplete dominant allele
HH

Question 24

What is a sex-linked gene?

Answer 24

a gene that appears on the portion of the X chromosome that is absent from the Y chromosome.

Question 25

What is an example of sex-linked recessive trait?

Answer 25

Haemophilia

Question 26

What is the characteristics associated with sex-linked recessive trait?

Answer 26

- 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 do show the trait

Question 27

What is the genotype of someone with the trait - sex-linked recessive trait

Answer 27

homozygous recessive male - X^hY female - X^hX^h

Question 28

What is the genotype of someone without the trait - sex-linked recessive trait

Answer 28

homozygous dominant male - X^HY female - X^HX heterozygous carrier females X^HX^h

Question 29

Why do sex-linked recessive gene affect males more than females?

Answer 29

As females have two X chromosomes, she would need two recessive alleles to express the recessive trait in her phenotype. Males have only one X chromosomes so they need only one recessive allele to express the recessive trait in his pheotype.

Question 30

What is an example of autosomal recessive inheritance?

Answer 30

Cystic Fibrosis (CF)

Question 31

What are the characteristics of autosomal recessive inheritance?

Answer 31

- the trait is expresed relatively rarely - the trait may skip generations - males and females are affected in approximately equal numbers

Question 32

What is the genotype of someone who had the trait - autosomal recessive

Answer 32

homozygous recessive cc

Question 33

What is the genotype of someone without the trait - autosomal recessive

Answer 33

homozygous dominant CC heterozygous (carrier) Cc

Question 34

What is an example of autosomal dominant inheritance?

Answer 34

Huntington's Chorea

Question 35

What are the characteristics associated with autosomal dominant inheritance?

Answer 35

- the trait appears in every generation - each person with the trait has an affected parent - males and females are affected in approximately equal numbers

Question 36

What is the genotype of someone with the trait - autosomal dominant

Answer 36

homozygous dominant or heterozygous CC or Cc

Question 37

What is the genotyped of someone without the trait - autosomal dominant

Answer 37

homozygous recessive cc