8: Genetics 2

Question 1

By which method can you check the whole genome for balanced mutations only?

Answer 1

Array CGH

Question 2

What are some examples of balanced chromosomal mutations?

Answer 2

Deletions

Duplications

Question 3

Apart from genetic testing, how else can you detect genetic diseases in a foetus?

Answer 3

Ultrasound

performed at 12 and 20 weeks

Question 4

What is trisomy 13 called?

Answer 4

Patau syndrome

Incompatible with life in most causes - lots of birth defects, failure of one or both eyes to develop (cylopsia)

Question 5

What are two common causes of intra-uterine growth restriction (IUGR)?

Answer 5

Chromosomal abnormality

Placental insufficiency

Question 6

Which causes of IUGR result in

a) symmetrical growth restriction
b) asymmetrical growth restriction?

Answer 6

a) Symmetrical IUGR suggests GENETIC DISORDER

b) Asymmetrical IUGR suggests PLACENTAL INSUFFICIENCY

Question 7

What is the appearance of asymmetrical IUGR secondary to placental insufficiency?

Why?

Answer 7

Enlarged head; smaller trunk and limbs

Brain growth prioritised

Question 8

What is the mode of inheritance of Duchenne muscular dystrophy?

Answer 8

X-linked recessive

Question 9

A woman carrying the recessive dystrophin mutation and an asymptomatic male have a child.

What is the percentage chance of them having an

a) affected child

b) affected boy?

Answer 9

a) 25% (recessive)
b) 50% (X-linked recessive, so can only be inherited by boys)

Question 10

What is the percentage risk that a child will inherit a

a) autosomal dominant
b) autosominal recessive disorder?

Answer 10

a) 50%

b) 25%

Question 11

The chances of a child inheriting an autosomal recessive disease is 25%.

In which group is this risk increased?

Answer 11

Consanguineous offspring

inbreeding

Question 12

Which percentage of foetuses have a congential disease?

Answer 12

0.05%

Relatively uncommon

Question 13

Which percentage of embryos have a genetic error before implantation?

Answer 13

50%

Question 14

Which method of genetic testing is the best for identifying a known gene mutation in a foetus?

Answer 14

NIPT

i.e taking a maternal blood sample and looking for foetal DNA

also useful for sex determination

Question 15

In cases of X-linked recessive disorders like DMD, why is non-invasive prenatal testing useful?

Answer 15

If NIPT identifies no Y chromosomes i.e it’s a girl, you can stop worrying because DMD is inherited by males only

Question 16

Which form of genetic testing involves work on embryos isolated from a woman?

Answer 16

Pre-implantation genetic diagnosis

Question 17

Pre-implantation genetic diagnosis (PGD) is often combined with which assisted conception therapies?

Answer 17

IVF

ICSI

Question 18

Which genetic analysis technique allows you to visualise the sex chromosomes of an embryo and thereby determine if it’s a boy or girl?

Answer 18

FISH

One of its few remaining uses - fluorescent probes

Question 19

What are the different names for the cell mass in the first days of embryogenesis?

Answer 19

Zygote

2 cell mass

4 cell mass

8 cell mass

Morula

Blastocyst

Question 20

From which stage of the embryo are cells taken for PIGD?

Answer 20

8 cell stage

Question 21

What is the success rate (“take-home rate”) of IVF?

Answer 21

30%

Which can be difficult for the parents to accept

Question 22

What is a major risk of IVF, which is avoided by not overstimulating the ovaries?

Answer 22

Multiple pregnancy

Question 23

Which genetic disorders are caused by

a) trisomy 13
b) trisomy 18
c) trisomy 21?

Answer 23

a) Patau syndrome

b) Edwards’ syndrome

c) Down’s syndrome

Question 24

revise week 5 endocrine and ivf process

Question 25

genetics terminology - come back to this, lots more to learn