Cytogenetics Flashcards
define cytogenetics
study genetic material (chromo) of cells
organisation of a karyogram
- length of chromosome: Lrg -> sml from 1 -> 22
- centromere position
- band pattern
genereal formal of karyotype (written)
chromosomes, gender (XX / XY), abnormal derivative (on # chromo)variation(chromo/s affected)
the 4 types of centromere positions
- metacentric: c.mere near middle: p = q
- sub-metacentric: closer to top end: p < q
- Acrocentric: c.mere at the top: p very small & have satellites (NOR region) on end
- Telocentric: centromere @ end = no p arm (*not present in human karyotype)
Describe the steps of peripheral blood harvest
- Blood cells CULTURED in growth media w/ phytohaemaglutanin (PHA) > stimulate lymphocytes to divide
- add HYPOTONIC KCl > RBC lyse & WBC swell
- ACETIC ACID > breakdown RBC & harden chromo
- FIX w/ methanol:acetic acid > harden & preserve chromo
things to consider when organising chromosomes in the karyogram
- size & shape
- centromere position
- banding pattern
Describe what constitutional & acquired cytogenetic changes are
- Constitutional changes: present in early FETAL development
* acquired: changes occur DURING life
2 cytogenetic changes (based on genetic info)
- Numerical: Aneuploid = # chromo varies (have extra or less)
- Structural: 1/+ structure of chrome altered
Nemonclature of abnormal derivatives/variation
- t = translocation
- inv = inversions
- dup = duplications
- del = deletions
- ins = insertions
- r = rings
- mar = makers = extrastructurally abnormal chromo - not ID by cytogen.
what are chromosome copy no. changes
- genome imbalance;
- Loss = deletion of chromo/gene
- Gain = duplication of chromo/gene
Describe Fluorescence in situ hybridisation (FISH)
- cell on metaphase or interphase stage
- DNA probes bind to specific known sequ. on chromo
- probes fluoresc
- limited colours
Types of probes
- REPETITIVE sequ probes
- CENTROMERIC or alpha stellite DNA probes
- WHOLE chromosome paints - UNIQUE sequ. probes (locus specific inserts): not repeated & may code for a gene
describe quantitiative Fluorescence PCR (QF-PCR)
- invasive sampling of amniotic fluid in preg women
- detect aenuploidies in fetal DNA
- multiplex PCR & gel capillary electro
characteristics of genetic markers (4)
- Short repeated sequ. of DNA located throughout genome
- polymorphic: # of repeated unit varies b/w indiv.
- Diploid organisms = 2 copies of any genetic marker
- can be used for genetic fingerprint (genotyping)
high resolution detection of copy no. changes: microarray & aCGH - compare them
- aCGH: hybridise normal reference DNA to patient DNA for comparison
- microarray: uses computer reference to compare & detect copy no. changes
