Final - Cytogenetics Flashcards
Clinical role of cytogenetics
- cytogenetics identifies chromosomal anomalies that may be associated with disease which contributed to the diagnosis and treatment of patients
- two categories of abnormalities = numerical and structural
Clinical specimens used in cytogenetics
- blood
- bone marrow
- tissue
- amniotic fluid
- chorionic villi
Specimen Preparations for Karyotyping
- Obtain sterile sample, transport biopsies on ice
- Alliquot into medium
- CO2 incubation
- Use of mitogen to encourage cell division and mitotic inhibitor to collect cells at metaphase
- Harvest via hypotonic solution to lyse cells
- Fix cells on slide
Histone
- an alkaline protein that package and order DNA into structural units = nucleosomes
Non-histone protein
- protein that remains after histones have been removed
ex: scaffold protein
Centromere
- a region of a chromosome to which spindle fibers attach during cell division.
- the location of a centromes gives a chromosome its characteristic shape.
- p = short arm, q= long arm
telomere
- short repeated DNA sequences located at each end of chromosomes
nucleosome
- a bead-like structure composed of histone proteins wrapped with DNA
metacentric
- centromere positioned in the middle of chromosome (centrally placed)
submetacentric
- describes a chromosome whose centromere is placed closer to one end than the other
acrocentric
- centromere placed very close to, but not at, one end
telocentric
- centromere located at the terminal end of the chromosome
3 criteria to classify and identify chromosomes
- Size
- Position of centromere
- Banding pattern
G-banding
- darkly stained G bands
- metaphase spreads are treated with trypsin and stained with Giemsa stain
- observed with light microscope
Q- banding
- bright flourescent bands under UV light same as darkly stained G bands
- uses chemical quinacrine mustard
C-banding
- darkly stained C band centromeric region of the chromosome corresponds to region of constitutive heterochromatin
- extract DNA from arms only so that when it is stained with Giemsa stain and observed under microscope, the centromere is stained.
Nomenclature
- Normal Female
- Normal Male
- Mosaic
- trisomy 13
- monosomy 8
- sex chromosome anomalies
- deletions
- additions
- translocations
- inversions
- # of chromosome, sex chromosomes
Normal Female: 46, XX
Normal Male: 46, XY
Mosaic: 45, X / 46, XX
Numerical anomalies-
trisomy 13: 47, XX, +13
monosomy 8: 45, XY, -8
sex chromosome anomalies: 45, X or 47, XXY
Structural anomalies-
deletions: 46, XX, del (4) (p 13.2)
additions: 46, XY, dup (11) (q11.2 q11.3)
translocations: 46, XY, t (4;9) (q21.2; p22)
inversions: 46, XY, inv (9) (p11 q21.1)
Nondisjunction
- the failure of homologous chromosomes to seperate properly during meiosis / mitosis
Aneuploidy
- gain/loss of chromosome equaling less than one complete complement
- ex: trisomy, monosomy
Trisomy
- 2n +1
- 3 copies of the same chromosome
Monosomy
- 2n -1
- 1 copy of a chromosome
Euploidy
- multiples of one complete chromosome complement
- haploid (n), diploid (2n), triploid (3n), tetraploid (4n)
- normal condition
Polyploidy
- a chromosomal number that is a multiple of the normal haploid chromosomal set
Down syndrome
Patau syndrome
Edwards syndrome
- trisomy 21
- trisomy 13
- trisomy 18
Structural anomalies
- deletion
- duplication
- translocation
- inversion
Deletion
- loss of a part of a chromosome leads to partial monosomy
- terminal or interstitial
Duplication
- additional copy of a chromosome segment
- results in partial trisomy
- terminal or interstitial
Translocation
- equal exchange involving segment with respect to the normal gene arrangment
Inversion
- reversal of a chromosomal segment with respect to the normal gene arrangment
- pericentric or paracentric
