- Created by: Hpgrice
- Created on: 31-10-19 10:53
What is cyto-genetics?
- Chromosome Analysis
- FISH test e.g. TBX1 gene in Chromosome 22 for Di George syndrome (most common microdeletion syndrome in the world)
- MLPA - Multiplexing PCR so mutliple tests can be ran on the same sampel
- Quatitative Fluorescent-PCR
- array CGH/SNP array
Cyto-genetics resolution is 5Mb and usually used cell culture and microscopy where as molecular genetics is 1bp and used DNA extraction and PCR.
Primary tissues for testing: blood, bone marrow, amniotic fluid, chorionic villus biopsies, skin biopsies.
37'C incubator, media that includes nutirents required and growth factors. For blood PHA which stimulates T-cells. Then add Colcemid (derived from kidney beans) to stop cell division at metaphase. The cells are then processed and the suspension is put onto a slide to view under the microscope or use a slide scanner which finds 120 metaphases per patient which reduces time.
Short arm = p (petit) and long arm = q
1.Metacentric - p arm and q arm are approx the same length e.g chromosomes 1,3,16,19 & 20
2. Sub-metacentric - p arm shorter than q arm e.g 4,5,17,18, most others
3. Acrocentric - satellite structure present on p arm, p arm very small e.g 13,14,15,21,22
X and Y are sex chromosomes, all others are autosomes
- Pre-treatment with proteolytic enzyme trypsin
- Dark bands - tightly packed, enzyme cannot degrade chromatin = gene poor
- Light bands - open structure, enzyme can degrade the chromatin = gene rich
- G-banding is very reproducible
Can change the amount of time cells have in colcemid in order to change resolution of the banding pattern.
Karyotyping has a resolution of 4-5Mb
Prenatal - 600 samples (400 CVS, 200 Amniotic fluid) and Postnatal case load - 1500 samples (venous blood, buccal swab)
Main reasons for referral:
Prenatal: pregnant women at risk of having a chromosomally abnormal baby.
- Two tests available: Chorionic villus biopsy where tissue is taken from the placenta and amniocentesis where fluid is taken from the sac surrounding the baby
- Need to have a risk of over 1/200 to have these invasive tests because there is 0.5% chance of miscarriage caused by the test
Prenatal case study
- 25ml of amniotic fluid. 0.5ml of amniotic fluid QF-PCR, rapid result (<48hours). 20+mls culture in flasks (>10 days)
- An abnormal QF-PCR result -> Karyotype, if normal QF-PCR results -> SNP array (better resolution)
- Look for the most common autosomal trisomy's: 13,18 and 21
QF-PCR gives you a graph with peaks to show where the alleles are located. 2 peaks = one maternal marker and one paternal marker, both are markers are slightly different. Can be the same marker which resutls in only one peak would show which is uninformative. 3 peaks shows that there are 2 alleles and therefore a trisomy.
Robertsonian Translocation - 2 chromosomes joined together.