3P: Cytogenetics I

Question 1

X inactivation

Answer 1

In the female, one X is inactivated randomly in the embryo

Question 2

X inactivation is an example of

Answer 2

Functional mosaicism

Question 3

How can we see the inactive X in interphase cells?

Answer 3

Appears as Barr body in granulocytes

Question 4

How can we identify a male by looking at the cells?

Answer 4

Using brilliant fluorescence to visualise Y-body

Question 5

To study metaphase chromosomes, two preparations can be used

Answer 5

• Direct: In-vivo dividing cells (e.g. bone marrow cells, tumor cells, intestinal ep.cells, cell lines, chorion/amnion cells)
• Indirect: In-vivo NON-dividing cells (G0), divide after in vitro stimulation (e.g. peripheral blood mononuclear cells)

Question 6

Indirect chromosome preparation

Answer 6

1. Blood (nucleated cells, e.g. WBC)
2. PHA (phetohemagglutinin)-> division induced, starts G0
3. Stop division in metaphase (using colcemid)
4. Use hypotonic solution -> the cells will swell
5. Fixation of the chromosomes with methylene
6. Cells are dropped, as they fall to the glass slide they will be next to each other
7. Staining of the chromosomes

Question 7

Arm ratio of chromosomes: p=q

Answer 7

Metacentric

Question 8

Arm ratio of chromosomes: p

Answer 8

Submetacentric

Question 9

Arm ratio of chromosomes: p<

Answer 9

Acrocentric

Question 10

Arm ratio of chromosomes: p=0

Answer 10

Telocentric (not in human)

Question 11

Karyogram

Answer 11

Set of metaphase chromosomes of an individual/patient (not always normal)

Question 12

Karyotype

Answer 12

The set of chromosomes which shows the normal set of chromosomes of a species

Question 13

Q-banding

Answer 13

Fluorochrome stained chromosomes, fades with time easily, analysis is difficult

Question 14

G-banding

Answer 14

Giemsa staining after chromosome denaturation, A-T rich regions are dark

Question 15

R-banding

Answer 15

Reverse of the G-bands (G- regions are visible)

Question 16

C-banding

Answer 16

Stains the centromere region highly repetitive heterochromatin

Question 17

NOR-silver staining

Answer 17

Stains the nucleolus organiser regions of the acrocentric chromosomes

Question 18

FISH to visualise a specific gene

Answer 18

1. Using heat to isolate the specific region, the structure will then be loose/open -> ssDNA
2. Use a probe with known nucleotides and a fluorescent dye
3. Fluorescent microscope

Question 19

Multicolor FISH (M-FISH)

Answer 19

24 different chromosome specific probes, each being labeled with one of five fluorochromes or a unique combination

Question 20

M-band

Answer 20

Different colors, compared with M-FISH that has one colour and G-band that has black and white