Cytogenetic tests

Question 1

Types of cells/tissue used for cytogenetic tests (and preparation)

Answer 1

Cells must be dividing for chromosomes to be visible so samples are treated with mitogens

Blood is treated with mitogen PHA and the T cells are studied

Amniotic fluid is treated with a medium and a substrate (contains skin cells)

Chorionic villus already has actively dividing cells

Question 2

Describe the 3 basic chromosome shapes

Answer 2

Metacentric - centromere in the middle, large or small, each half is a chromatid

Submetacentric - centromere towards one end; short arms (p) found above ; long arms (q) found below

Acrocentric - centromere very close to one end ; may have satellites separated from the small short arms by a secondary constriction or satellite stalk

Question 3

What is X-inactivation

Answer 3

Females carry two copies of the genes on the X chromosome
X-inactivation ensures only one copy of the X chromosome is transcribed by switching off one copy
Occurs 2 weeks post fertilisation
Occurs randomly within stem cells

Question 4

What is F.I.S.H ?

Answer 4

Fluorescence In Situ Hybridisation
Segment of single stranded DNA is labelled with fluorescent tag
Hybridises with its matching sequence

Question 5

Edwards syndrome - symptoms

Answer 5

Growth retardation
Prominent occipital (back of head)
Small mouth , clenched hands, overlapping fingers
Prominent heels
Congenital heart disease and renal abnormalities in some
50% die by 2 months

Question 6

Patau syndrome symptoms

Answer 6

Scalp defect 
Hypo telos so (narrow eyes)
Polydactyl 
Holoprosencephaly (brain malformation)
Bilateral cleft lip and palate 
Congenital heart disease
Renal abnormalities 
70% die by 6 months

Question 7

Examples of trisomy’s

Answer 7

Downs is mostly trisomy 21
Edwards is trisomy 18
Palau’s is trisomy 13

Question 8

Example of monosomys

Answer 8

Only one monosomy is possible - monosomy of the X chromosome (Turner syndrome)