Cytogenetic Tests Flashcards

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1
Q

Cytogenetics

A

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

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2
Q

Cell/tissue used for constitutional cytogenetics

A

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

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3
Q

Cell/tissue used for malignancy cytogenetics

A

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

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4
Q

Shapes of chromosomes in metaphase

A
  1. metacentric
  2. submetacentric
  3. acrocentric
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5
Q

Metacentric

A

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

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6
Q

Submetacentric

A
centromere towards one end
short arms (p) upper
long arms (q) below
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7
Q

Acrocentric

A

centromere very close to one end

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

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8
Q

What is each arm of a chromosome divided into?

A

subdivided into G-bands numbered from the centromere outwards

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9
Q

Fluorescence in situ hybridisation

A

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

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10
Q

Difference between X and Y chromosome

A

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

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11
Q

Dosage disequilibrium

A

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

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12
Q

Types of chromosome abnormality

A
  1. numerical: trisomy, polyploidy
  2. uniparental origin: uniparental disomy
  3. structural: translocation, deletion, duplication, marker
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13
Q

Down Syndrome cause

A
  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
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14
Q

Features of DS

A
flat facial profile, flat back of head, protruding tongue
mild-moderate mental retardation
autism
cardiac defects
increased risk of leukaemia
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15
Q

Edwards syndrome cause

A

trisomy 18

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16
Q

Features of ES

A

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

17
Q

Patall syndrome cause

A

trisomy 13

18
Q

PS features

A

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

19
Q

Turner syndrome cause

A

monosomy of X chromosome

20
Q

TS features

A

short structure, lymphoeddema of hands and feet

bicuspid aortic valve, webbed neck

21
Q

Examples of uniparental disomy, deletion

A
  1. Prader-Willi syndrome: chromosome 15, maternal UPD,
    paternal deletion
  2. Angelman syndrome: chromosome 15, paternal UPD,
    maternal deletion
22
Q

Examples of cytogenic referral

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