Unit 2.4 - Antenatal And Postnatal Screening

Question 1

What does antenatal screening do?

Answer 1

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

Question 2

What are techniques used to monitor the health of the mother and developing foetus?

Answer 2

Ultra sound imaging:
• anomaly scan may detect serious physical abnormalities in the foetus
•dating scans for pregnancy strange and due date, are used with tests for marker chemicals which vary normally during pregnancy
Routine blood and urine tests are Carried out throughout pregnancy to monitor the concentrations of marker chemicals

Question 3

When do dating and anomaly scans take place?

Answer 3

Dating scan - 8 to 14 weeks

Anomaly scan - 18 to 20 weeks

Question 4

For blood and urine tests what could measuring a chemical at the wrong time lead to?

Answer 4

A false positive result

Question 5

What can an atypical chemical concentration lead to?

Answer 5

Diagnostic testing to determine if the foetus has a medical condition

Question 6

What are the benefits and disadvantages of amniocentesis and CVS?

Answer 6

• CVS can be carried out in early pregnancy then amniocentesis
• CVS has a higher risk of miscarry

Question 7

What can the sales samples from the diagnostic testing do?

Answer 7

Can be cultured to obtain sufficient cells to produce a karyotype to diagnose a range of conditions

Question 8

What does a karyotype show?

Answer 8

An individuals chromosomes arranged as homologous pairs

Question 9

What can postnatal screening be used for?

Answer 9

Diagnostic testing for phenylketonuria ( PKU)

Question 10

What happens in PKU?

Answer 10

• A substitution mutation means that the enzyme which converts phenylalanine to tyrosine is non functional
• Individuals with high levels of phenylalanine are placed on a restricted diet

Question 11

Explain the use of patterns of inheritance in genetic screening

Answer 11

• A pedigree chart can be used to analyse patterns of inheritance in genetic screening
• A pattern of inheritance can be revealed by collecting information about a particular characteristic from family members and the information used to construct a family tree
• Once the phenotypes are known then most of the genotypes can be determined

Question 12

How can patterns of inheritance be used in counselling?

Answer 12

Construction of a family tree is carried out by a genetic councillor and the information is used to advise parents of the possibility of passing a genetic condition to their child

Question 13

What are autosomes?

Answer 13

All other chromosomes that are no X and Y chromosomes ( sex chromosomes)

Question 14

What does dominant mean?

Answer 14

When only one dominant allele is required to show up in the phenotype

Question 15

What does recessive mean?

Answer 15

When two recessive alleles are required to show up in the phenotypes

Question 16

What are autosomal recessive conditions controlled by?

Answer 16

Genes found on the autosomes and are recessive

Question 17

What are the characteristics of autosomal recessive?

Answer 17

It’s rare in occurrence
It may skip generations
It occurs equally in men and woman

Question 18

What is an example of an autosomal recessive disorder?

Answer 18

Cystic fibrosis

Question 19

What are autosomal dominant conditions controlled by?

Answer 19

Genes found on the autosomes and are dominant

Question 20

What are characteristics of autosomal dominant inheritance?

Answer 20

• it appears in every generation
• affected individuals have an affected parent
• males and females are affected in roughly equal numbers

Question 21

What is an example of a autosomal dominant disorder?

Answer 21

Huntington’s disease

Question 22

When does autosomal incomplete dominance occur?

Answer 22

When one allele is not completely dominant over the other

These alleles are both given a capital letter to denote they are incompletely dominant

Question 23

What are the characteristics of autosomal incomplete dominance?

Answer 23

• The fully expressed form is very rare
• The partly expressed form is more common
• Males and females are equally affected

Question 24

What is an example of incomplete dominance?

Answer 24

Sickle cell anaemia

Question 25

What genes are sex linked?

Answer 25

Genes present on the X chromosome are absent from the Y chromosome

Question 26

What happens to the sex linked genes carried on the X chromosome of a male organism?

Answer 26

• It will always be expressed in the phenotype

* It does not matter if they are dominant or recessive, because there is no alleles of the gene on the Y chromosome

Question 27

What an example of a sex-linked gene?

Answer 27

Colour vision

Question 28

What happens to a female known as a carrier?

Answer 28

• She is not effected herself but has a 50% chance of passing on the colour blindness allele to each of her offspring
• That means 50% of her daughters may be carriers and 50% of her sons will be colour blind

Question 29

What are the characteristics of sex-linked recessive?

Answer 29

• More males affected than females
• An effected male does not have any affected sons
• An effected male may have effected grandsons