Example of a deletion syndrome - Terminal - Interstitial

- Terminal: Cri du chat syndrome (5p-) - Interstitial: Williams syndrome (7q-) These are microdeletions - have to use FISH to recognize Deletions can be due to uneven crossing over -> deletion in one chr. and duplication in the other Deletions can give partial monosomy

5P. Cytogenetics Flashcards by JR SV

Structure and types of eukaryotic chromosome

Short arm: p =petit
Long arm: q

Types:

1) Metacentric
2) Submetacentric
3) Acrocentric (13, 14, 15, 21, 22)
4) (Telocentric - not in humans)

How well did you know this?

Not at all

Perfectly

Karyotyping: chromosome preparation

a) Direct
- From in-vivo dividing cells
b) Indirect
- From in-vivo non-dividing cells (G0)
- Divide after in-vitro stimulation
- Procedure:
1. Add tissue sample (peripheral blood)
2. Stimulate mitosis with PHA
3. Incubate (2-3 days)
4. Add colcemid to stop mitosis in metaphase
5. Transfer cells and centrifuge
6. Hypotonic saline
7. Add fixative
8. Drop onto slide
9. View in microscope + take picture

*View with Giemsa stain

How well did you know this?

Not at all

Perfectly

Karyotyping: principle and significance

How well did you know this?

Not at all

Perfectly

Karyotyping: types of banding techniques

Q-banding (not so good)
Quinacrine mustard
Fluorochrome stained chromosomes
Brilliant fluorescence of Y-chromosome

G-banding

Giemsa after chromosome denautartion
A-T regions dark (SAR attachment - Giemsa stains SAR)

R-banding
- Reverse of G-banding

C banding
- Stains centromeric heterochromatin

NOR-silver staining

How well did you know this?

Not at all

Perfectly

Karyotyping: principle and significance of multicolour-FISH = spectral karyotyping-SKY

FISH: specific for a gene, chromosome region or chromosome

Multicolor-FISH (M-FISH): can show all chromosome/separate between them in 1 hybridization experiment

5 flourochromes in different combinations
Show chromosome territories
Show f.ex translocations

How well did you know this?

Not at all

Perfectly

Karyotyping: principle and significance of M-banding

5-10 overlapping fragments per chromosome are cut out by microdissection -> amplified ->region-specific library
Hybridization probes made based on library, and labelled by different fluorochromes
Overlapping areas gets different shades from original probes => can see all bands

How well did you know this?

Not at all

Perfectly

X inactivation result on blood smear

Barr body (drumstick) in granulocyte or neurons

How well did you know this?

Not at all

Perfectly

Study of sex chromosomes in interphase

Barr body in females

Y-body

How well did you know this?

Not at all

Perfectly

Characteristics of human karyotype

44 autosomes + 2 sex chromosomes

5 pairs of acrosomal chromosomes: 13, 14, 15, 21, 22

How well did you know this?

Not at all

Perfectly

Mutagenicity tests (practice presentation)

Sister chromatid exchange (SCE) detection

Detection: block in metaphase -> hypotonization, fixation -> Hoechst 33258 -> UV light -> heat, Giemsa
Criss cross pattern in chromosome if exchanged
Good for diagnosis of chromosome breakage syndromes like Bloom syndrome

Micronucleus analysis

How well did you know this?

Not at all

Perfectly

Cytogenetics definition

The study of chromosome number, structure and function

How well did you know this?

Not at all

Perfectly

Chromosome theories + how to check

1) Chromosome territory model
- Chromosomes occupy distinct territories
2) Random organization model
- Chromatin fibres of each chromosome randomly distributed throughout nucleus

Check with laser damage

1) Small subset of chromosomes damaged
2) Many and random chromosomes damaged
* Chromosome territory model most correct

How well did you know this?

Not at all

Perfectly

Structural chromosome abnormalities

1) Deletion (loss)
2) Translocations (neutral)
3) Inversions (neutral)
4) Insertions (neutral)
5) Ring chromosomes
6) Isochromosomes
(7. duplication - gain)
* Gode filmer på youtube (UCD medicine)

How well did you know this?

Not at all

Perfectly

Example of a deletion syndrome

Terminal
Interstitial

Terminal: Cri du chat syndrome (5p-)
Interstitial: Williams syndrome (7q-)
These are microdeletions - have to use FISH to recognize
Deletions can be due to uneven crossing over -> deletion in one chr. and duplication in the other
Deletions can give partial monosomy

How well did you know this?

Not at all

Perfectly

Examples of microdeletions + how to recognize

Recognize with FISH

Cri-du-chat (5p-)
DiGeorge SY (22q-)
Kallman SY
Williams SY (7q-)
Prader-Willi/Angelman SY (15q-)
Miller-Dieker SY (17q-)
Smith-Magenis SY
Steroid sulfatase deficiency
Wolf-Hirschhorn

How well did you know this?

Not at all

Perfectly

Characteristics of chromosomal translocations

Def: chromosomes breaks and the fragments rejoin to other chromosomes

Usually reciprocal
NO loss or addition of genetic material - only exchange
No problem if in a noncoding region
Can cause reduction in fertility

How well did you know this?

Not at all

Perfectly

Types of translocations

1) Reciprocal
2) Robertsonian (centric fusion)
3) Insertional

How well did you know this?

Not at all

Perfectly

Reciprocal translocation

Balanced translocation (no material lost or gained)
Can occur between any two chromosomes
Healthy - but infertility can occur (problems in pairing/segregation during meiosis)

How well did you know this?

Not at all

Perfectly

Segregation types in reciprocal translocation + outcome of daughter cells

1) Alternate segregation
- 2 normal cells + 2 balanced translocation cells
2) Adjacent 1 segregation
- All 4 cells unbalanced
3) Adjacent 2 segregation
- All 4 cells unbalanced

How well did you know this?

Not at all

Perfectly

Examples of reciprocal translocations

Study These Flashcards

1) t (9;22) - Philadelphia chromosome
- Bcr-abl fusion gene (hyperactive -> increased cell prolif)
- Depending on breakpoint: CML or ALL
2) t (11;22) - Ewing sarcoma (FLI1-EWSR1)
3) t (15;17) - Acute promyelocytic leukemia (PML-RARA)
4) t (8;14) - Burkitt’s lymphoma (IgH-cMyc)

Robertsonian translocation characteristics

Study These Flashcards

Also called centric fusions
In ACROCENTRIC chromosomes
Gives a karyotype with 1 less chromosome
Healty - but mild reduction in fertility
If translocated chr is passed on with a normal chr -> trisomy (13-Patau, 14-lethal, 15-lethal, 21-Downs, 22-lethal)

Acrocentric chromosomes

Study These Flashcards

Chr 13, 14, 15, 21, 22

- NOR (nucleolar organizing region = repetitive rDNA)

Inversions characteristics

Study These Flashcards

2 breaks -> piece is turned upside down
Types:
a) Paracentric: centromere not involved
b) Pericentric: centromere involved
Both can cause problems in meiotic pairing and segregation

Paracentric inversion

Study These Flashcards

Paracentric: centromere not involved
When crossing over in meiosis - one chr forms a loop to pair correct genes, hence you can get:
1) Normal chromatid
2) Dicentric chromatid: 2 centromeres (dupl+del of genes)
3) Inversion chromatid
4) Acentric chromatid: no centromeres
* Se film på youtube UCD medicine

Pericentric inversion

Pericentric: centromere involved When crossing over in meiosis - one chr forms a loop to pair correct genes, hence you can get: 1) Normal chromatid 2) Abnormal chromatid: duplication+deletion of genes 3) Inversion chromatid 4) Abnormal: deletion+duplication of genes (opposite genes of 2)

Ring chromosomes characteristics

- Break removes both telomeres - Ends fuse together -> ring - Symptoms depend on extent of deletion - Mitotically stable - Replication (meiosis) often problematic - Partial monosomy in many

Isochromosomes characteristics

- Chromosomes split "the wrong way" (horizontally) in mitosis or meiosis II - Result: both long arms stick together + both short arms stick together (-> deletions+duplications) - Poor prognosis - except: iXq -> Turner syndrome

Hemophilia A cause

Intrachromosomal rearrangement -> no factor VIII

Numerical chromosome aberrations

Ploidy - Monosomy - Trisomy - Triploidy

Euploidy

Normal number of structurally normal chromosomes (46)

Aneuploidy definition+types

Less or more than the normal diploid number * Most frequent cytogenetic abnormality 1) Monosomy 2) Trisomy

Monosomy characteristics

- Lack of one of a pair of chromosomes - Turner syndrome (X0) - only viable monosomy - Due to non-disjunction in meiosis I or II

Nondisjunction meiosis results + causes

1) Result: monosomy or trisomy * Meiosis I: premature homologue- or sister chr separatation - > All zygotes abnormal (2 mono-, 2 trisomy) * Meiosis II: premature sister chromatid separation - >2 zygotes abnormal (1 mono-, 1 trisomy) 2) Causes: - Mitosic checkpoint defect - Cohesion defect - Merotelic attachment - Multipolar mitotic divisions

Trisomy characteristics

1 extra chromosome in a pair - Trisomy 13: Patau syndrome - Trisomy 18: Edward's syndrome - Trisomy 21: Down syndrome

Triploidy characteristics

``` 3 copies of EVERY chromosome (69 chromosomes) Causes: 1) 2 sperms fertilize 2) Diploid sperm fertilize 3) Diploid ovum fertilized Survivors are usually mosiac ```

Down syndrome

Trisomy 21 - Can also be caused by unbalanced Robertsonian translocation - Midpalmar crease often seen

Sex chromosome abnormalities

1) XO: Turner (sympt: pterygium colli - "webbed neck") 2) XXY: Klinefelter 3) XXX: Triplo-X 4) XYY: Jacob's syndrome ("superman") 5) XXYY: XXYY syndrome

Uniparental disomy (UPD)

"Both homologues from 1 parent, none from the other" Occurs due to nondisjunction -> trisomy -> "trisomic rescue" = 1 chromosome deleted -> If deleted chromosome was from the "normal" parent -> UPD - 1st meiotic division nondisjunction: heterodisomy - 2nd meiotic division nondisjunction: isosomy

Mosaicism

An individual with more than one cytogenetically distinct population of cells with the same origin - Large proportion of abnormal cells -> disease - Most of Turner SY patients die before birth, but mosaicism are found in many survivors (many normal cells) - X-chr mosaicism: in females - inactivation of either maternal or paternal X in different cells

Chimera

An individual with more than one cytogenetically distinct population of cells with different origin

Microchimerism

Presence of a small number of cells that originate from another individual and are therefore genetically distinct from the cells of the host individual - Pregnancy is the major natural source

Preimplantation embryos

Higher number of chromosomal abnormalities

Most common trisomy

Trisomy 16 | *But lethal -> spontaneous abortion

Spontaneous abortions

- 50 % involve chromosomal abnormalities | - About 15 % of recognized pregnancies end in spontaneous abortion or miscarriage

Clinical presentation suggestive of chromosomal abnormality

1) Infertility/sterlity 2) Intersexes (genetic & phenotypic sex not same) 3) Multiple congenital malformations (esp. del & aneupl) 4) Mental retardation (ex: Down & Fragile X)

Fluorochrome probes

1) DEAC: blue 2) FITC: green 3) Spectrum Orange: red 4) Texas red: pink 5) Cy5: yellow

qh+

Excess of centric heterochromatin in the lomg arm: chromosome polymorphism - On chr 1, 9, 16 or Y

Microdeletions/microduplications detection

Not detectable with banded karyotyping | - Must use FISH

Burkitt lymphoma translocations

t(2;8) t(8;14) t(8;22)

5P. Cytogenetics Flashcards

(49 cards)