a display or photomicrograph of an individual’s somatic-cell metaphase chromosomes that are...

• A display or photomicrograph of an individual’s somatic-cell metaphase chromosomes that are arranged in a standard sequence (usually based on number, size, and type)

• Three key features to identify chromosomes similarities and differences:

1. Size. This is the easiest way to tell two different chromosomes apart.

2. Banding pattern. The size and location of Giemsa bands on chromosomes make each chromosome pair unique.

3. Centromere position. Centromeres are regions in chromosomes that appear as a constriction.

• Metacentric chromosomes, the centromere lies near the center of the chromosome.

• Submetacentric , have a centromere that is off-center, so that one chromosome arm is longer than the other.

• Acrocentric chromosomes, the centromere resides very near one end.

GroupChromosomesDescription

A1–3Largest; 1 and 3 are metacentric but 2 is submetacentric

B4,5Large; submetacentric with two arms very different in size

C6–12,XMedium size; submetacentric

D13–15Medium size; acrocentric

E16–18Small; 16 is metacentric but 17 and 18 are submetacentric

F19,20Small; metacentric

G21,22,YSmall; acrocentric

Autosomes are numbered from largest to smallest, except that chromosome 21 is smaller than chromosome 22.

• Chromosomes are stained with various dyes enabling the chromosome segments to be identified

• G – Banding • It is a technique used in cytogenetics to produce a

visible karyotype by staining condensed chromosomes by Giemsa stain or dye.

• The Dye gives chromosomes a striped appearance because it stains the regions of DNA that are rich in adenine (A) and thymine (T) base pairs.

• The Dye stains the regions of DNA that are rich in adenine (A) and thymine (T) base pairs.

• AT rich regions appear as Dark bands ( G+ bands)• AT Poor regions appear as Light bands (G- bands)

• SPECIMENS USED

Peripheral Blood Cultured Skin Fibroblast

Bone Marrow Amniotic Fluid

• SPECIMENS USED

Product of conception (POV)

1. Vinous Blood collection with sterile condetions in Heparine tube but not EDTA

2. Cell culture (the target cells are the lymphocytes) Culture the blood samples (lymphocytes)in a growth medium for 2 – 3 days at 37 degree and stimulate mitosis

• The growth culture contains A growth base like RPMI L-glutamine support cell growth Bovine serum albumine Antibiotics Phytohaemagglutinin as lymphocytes growth stimulus or mitogen

3. Stopping the cell division at Metaphase by adding Colchicine after 72 hours,

Colchicine stops the cell division by inhibiting

the microtubules polymerization at the Metaphase so that the chromosomes sticks in the metaphase and do not separate

4. Hypotonic treatment of red & white blood cells

• Potassium chloride

• This solution causes the white blood cells to swell so that the chromosomes will spread when added to a slide as well as lyses the red blood cells. After the cells have been allowed to sit in hypotonic solution

5. Fixation : the cells are Fixed a solution which contain (3:1 methanol to glacial acetic acid)

6. Slides preparation A. Dropping the swelled & fixed cells on the glass

slides by pasture pipit this leads to cells explosion and the chromosomes spreads on the slides

B. Air dry of the slides C. Heat dry at oven

7. Slides staining

• Using Giemsa stain that stains the AT rich regions and establish the banding pattern of the chromosomes

• Search for a good 10 – 20 views • Select the chromosomes one by one and do the

following

1. Count the number of chromosome in each view field

2. Draw them on a paper (now days by using the digital camera the technician can take a photo for the field)

3. Arrange them in order by writing the order or number of each chromosome near it on the paper (now days this is computerized)