Cytogenetic Tests

Question 1

Cytogenetics

Answer 1

genetics concerned with how the choromosomes relate to cell behaviour, particularly mitosis and meiosis

Question 2

Cell/tissue used for constitutional cytogenetics

Answer 2

postnatal - blood, not active, mitogen PHA, T cells
prenatal - amniotic fluid, inactive, medium and substrate
- chorionic villus, actively dividing cells from the
placenta

Question 3

Cell/tissue used for malignancy cytogenetics

Answer 3

leukaemia: bone marrow, blood if leukaemia cells
present
lymphoma: lymph node biopsy, bone marrow
other tumours: tumour biopsy, bone marrow

Question 4

Shapes of chromosomes in metaphase

Answer 4

1. metacentric
2. submetacentric
3. acrocentric

Question 5

Metacentric

Answer 5

centromere in middle
large/small
each half of the metaphase chromosome is a chromatic

Question 6

Submetacentric

Answer 6

centromere towards one end
short arms (p) upper
long arms (q) below

Question 7

Acrocentric

Answer 7

centromere very close to one end

may have satellites separated from the small short arms by a secondary constriction/satellite stalk

Question 8

What is each arm of a chromosome divided into?

Answer 8

subdivided into G-bands numbered from the centromere outwards

Question 9

Fluorescence in situ hybridisation

Answer 9

segment on single-stranded DNA labelled with fluorescent tag
hybridised to target DNA attached to a slide
hybridises with matching DNA sequence
detect chromosome abnormalities

Question 10

Difference between X and Y chromosome

Answer 10

X: larger, 195 known gene loci
Y: 50mb, around 13 known loci

Question 11

Dosage disequilibrium

Answer 11

females have 2 copies on X chromosomes, male only 1 copy of genes
X inactivation re-balances by ‘switching off’ 1 copy

Question 12

Types of chromosome abnormality

Answer 12

1. numerical: trisomy, polyploidy
2. uniparental origin: uniparental disomy
3. structural: translocation, deletion, duplication, marker

Question 13

Down Syndrome cause

Answer 13

1. trisomy 21: majority due to non-disjunction at maternal meiotic 1st division
2. unbalanced robertsonian translocation: inherited from balanced robertsonian carrier parent
3. mosaic: post-zygotic, mitotic non-disjunction event

Question 14

Features of DS

Answer 14

flat facial profile, flat back of head, protruding tongue
mild-moderate mental retardation
autism
cardiac defects
increased risk of leukaemia

Question 15

Edwards syndrome cause

Answer 15

trisomy 18

Question 16

Features of ES

Answer 16

growth retardation, prominent occiput
congenital heart disease
rocker bottom feet
overlapping fingers, small mouth, clenched hands

Question 17

Patall syndrome cause

Answer 17

trisomy 13

Question 18

PS features

Answer 18

scalp defects, polydactyly, cleft lip
congenital heart disease, undescended testes
majority die by 6 months

Question 19

Turner syndrome cause

Answer 19

monosomy of X chromosome

Question 20

TS features

Answer 20

short structure, lymphoeddema of hands and feet

bicuspid aortic valve, webbed neck

Question 21

Examples of uniparental disomy, deletion

Answer 21

1. Prader-Willi syndrome: chromosome 15, maternal UPD,
   paternal deletion
2. Angelman syndrome: chromosome 15, paternal UPD,
   maternal deletion

Question 22

Examples of cytogenic referral

Answer 22

1. learning difficulties/congenital abnormalities
2. recurrent miscarriage
3. infertility
4. prenatal diagnosis