Week 20 of SIP: Last Posting

Name: Hardina Bte Hamzah
Topic: Cytogenetics

Structural Abnormalities of Chromosomes

When chromosomes have replicated and are waiting to be separated into 2 daughter cells, chromosome breakage is frequently accompanied by exchange material from one chromatid to another. The exchange of material occurs during the pachytene period of the first meiotic division and is a mechanism built into the reproductive cycle to ensure the mixing of the gene pool. The exchange is called crossing over and it occurs when paired homologs form chiasmata. The abnormailties occur when the chromosomes break at non-homologous sites leading to unequal exchanges. 2 major classes of detectable rearrangements are rearrangements within a single chromosome and rearrangements involving more than 1 chromosome.

Examples of rearrangements within a single chromosome:

Deletion is a loss of chromosomal material. An interstitial deletion can arise from unequal crossing over at meiosis. Breaks can occur in 2 homologs at slightly different positions on the chromosomes and the pieces can be reconnected to the alternate chromosome. One chromosome could lose material while the other could gain material. This kind of mechanism is more likely to occur. Cri-du-chat syndrome is one of the examples of syndromes resulting from deletion.

Duplication occurs when a portion of one homolog may be present in duplicate. A duplicated segment may be inserted in the same order as the original segment. However, we cannot identify which piece was original. It can also become reversed. Duplication in the same order which also can be known as tandem duplication may probably results from unequal crossing over in meiosis or from a rearrangement between 2 chromatids during mitosis. Any duplication represents a trisomic state for whatever gene loci are present on the affected segment.

Inversion is a two-break structural irregularity that affects a single chromosome. The segment between the 2 breaks rotates 180 degrees and reattaches to the points of breakage. There are 2 types of inversion: Paracentric and Pericentric. In paracentric inversions, the centromere is not included in inverted segment and the arm ratio of the chromosome remains the same. In pericentric inversions, the inverted portion does include the centromere and the arm ratio may be changed.

Examples of rearrangements involving more than 1 chromosome:

Translocation is an exchange of genetic material between 2 or more non-homologous chromosomes. It is an abnormal mechanism but it can occur when 2 or more chromosomes break at the same time. Broken chromosome ends are regarded as sticky and can attract the cellular enzymatic repair service. Usually broken ends stay close to each other and are reunited. However, it is possible to mismatch the broken ends. The carrier of a balanced translocation may pass on the only part of the translocation which can result in genetically unbalanced offspring.

Dicentric chromosome possesses 2 centromeres and it is a result of the joining of homologous chromatids to form an isochromosome. An isochromosome is a chromosome in which the arms n either side of the centromere are morphologically identical ad bear the same gene loci. Dicentrics may cause problems during cell division, however, if the 2 centromeres are far apart on the derivative chromosome. If both centromeres are active, they can be drawn to opposite poles of the spindle resulting in formation of an anaphase bridge. Anaphase bridge is a chromosome that makes a bridge between 2 daughter cells at anaphase. When this happens, the dicentric can be left outside both daughter nuclei as they form or can break apart and cause loss or gain of chromosomal material.

Insertion is an addition of genetic material between 2 normally adjacent sections of a chromosome. The additional material could be a duplication of a section of the same chromosome but is more likely to come from a different chromosome. Insertions are difficult to identify unless there is a complementary deletion in the cell.

WEEK 19 Posting

Architect system analyser (ci8200)

Picture taken from: http://www.drdangslab.com/images/eqiupments/ci8200.jpg



Introduction

The modular design of the ARCHITECT family of analysers allow multiple processing modules which perform all sample processing activities, to be physically joined to form a single workstation or system. These ARCHITECT systems can be configured to process sample using potentiometric and photometric methoeds and/or chemiluminescent microparticle immunoassay (CMIA) methods.

The ARCHITECT ci8200 analyser is composed of two modules, which is c8000 and i2000. C8000 module is using the potentiometric and photometric methos while the i2000 module uses CMIA method.

Here are the majority tests carried out the ARCHITECT analyser and their reference range:


1. Free Thyroxine (FT4) 10.0-20.0pmol/L
2. Total Triidothyroninn (Total T3) 1.2-2.3 nmol/L
3. Anti-TPO <5.6IU/ml
4. Anti-Tg <4.11u/ml
5. Alpha-fetoprotein (AFP) 1.0-10.0ug/L
6. Carcinoembroynic Antigen (CEA) 0.0-5.0ug/L
7. Vitamin B12 (B12) 132-835 pmol/L
8. Folate (FA) 7.40nmol/L
9. Ferritin 30-323ug/L M (0-30Y) 32-294ug/L M (31Y & Above) 7.6-179ug/L F (premenopausal) 182-339ug/L F (postmenopausal)
10. Syphilis non-reactive
11. HBsAg non reactive
12. HbeAg non-reactive
13. Anti-HCV non-reactive
14. Anti-HAV IgM non-reactive
15. HAV AB non-reactive
16. Anti-HBs non-reactive
17. HIV Ag/Ab Combo non-reactive
18. Kappa light chains 1.40-3.8g/L
19. Lambda light chains 0.90-2.50g/L
20. Immunoglobulin A 0.8-4.0g/L
21. Immunoglobulin G 5.0-15.0g/L
22. Immunoglobulin M 0.3-3.0g/L
23. Rheumatoid Factor <20.0 IU/L
24. Transferrin 1.74-3.64g/L Spectrophotometric method
25. Iron F 11.27 umol M 11.29umol/L

The analyser uses these three methods to measure the concentration of analytes in sample.

1. Photometry method

Phtometry method uses
-End point assay are reactions that reach an equilibrium and at that time there is little or no further change to the absorbance readings. During this equilibrium time, the system measures the absorbance readings used for calibration and calculating results.

-Rate assay are reactions that measure the constant change in absorbance over time. The system performs readings several times during this reaction, calculates absorbance change (activity), and then uses the readings to calculate results.

2. Potentiometry (measures electrical potential in sample)

-The c8000 modules uses an ICT (integrated chip technology) modules to measure potentiometric assay (eleytrolytes). ICT methodology uses the solid state ion-selective electrodes contained in a single chip that reduces the maintenance require to perform electrolytes measurements.

3. Chemiluminescent technology

-During sample processing, microparticles (paramagnetic microparticles coated with capture molecules) are mixed with the sample binds to the corresponding capture molecules on the microparticles, forming the immune complex.
-After incubation, a magnet attracts the paramagnetic microparticles (bound to the surface analyte) to a wall of the reaction vessel. The reaction mixture is washed to remove unbound materials, further processing can now take place.
-Detection of ther eaction mixture in the reaction vessel is accomplished with a chemiluminescent acridinium-labeled conjugate. The conjugate binds to the immune complex to complete the reaction mixture.
-After incubation, the reaction micture is washed to remove unbound material. The pre-trigger solution is added and a background read is taken.
-Pre-trigger performs the following functions: - Create an acidic anvironment to prevent early release of the energy(light emission). Helps to keep microparticles from clumping. - Splits acridinium dye off the conjugate bound to the microparticle complex. This prepares the acridinium dye for the nest step.
- The system then adds Trigger solution to the reaction mixture. The acridinium alkaline solution. This causes the chemiluminescent reaction to occur. N-methylacridne is formed and releases energy (light emission) as it returns to its ground state. The CMIA optical assembly measures the chemiluminescent emissin (activated red) over a predefined time perioed to quantitate the analyte concentration or to determine qualitative interpretations for index cut-off assay.

Specimen

-Human serum (including serum collected in serum separator tubes) or plasma collected in sodium heparin, lithium heparin separator tubes, or potassium EDTA anticoagulant tubes may be used. Other anticoagulants have nor been validated for use with ARCHITECT.

Method
1. Specimen are spun via the centrifuge for 5minutes.
2. The cap of the specimen tube is removed.
3. Specimen placed on the ARCHITECT rack.
4. Rack loaded into the ARCHITECT.
5. Test are run.

So that's all for my last posting.

Thanks for reading.

Dyana
0605169B