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Genetics 2017 > 5P. Cytogenetics > Flashcards

5P. Cytogenetics Flashcards

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1
Q

Structure and types of eukaryotic chromosome

A

Short arm: p =petit
Long arm: q

Types:

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

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2
Q

Karyotyping: chromosome preparation

A

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

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3
Q

Karyotyping: principle and significance

A

k

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4
Q

Karyotyping: types of banding techniques

A
  • 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

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5
Q

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

A

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
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6
Q

Karyotyping: principle and significance of M-banding

A
  • 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
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7
Q

X inactivation result on blood smear

A

Barr body (drumstick) in granulocyte or neurons

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8
Q

Study of sex chromosomes in interphase

A

Barr body in females

Y-body

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9
Q

Characteristics of human karyotype

A

44 autosomes + 2 sex chromosomes

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

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10
Q

Mutagenicity tests (practice presentation)

A

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

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11
Q

Cytogenetics definition

A

The study of chromosome number, structure and function

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12
Q

Chromosome theories + how to check

A

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

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13
Q

Structural chromosome abnormalities

A

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)

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14
Q

Example of a deletion syndrome

  • Terminal
  • Interstitial
A
  • 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
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15
Q

Examples of microdeletions + how to recognize

A

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
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16
Q

Characteristics of chromosomal translocations

A

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
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17
Q

Types of translocations

A

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

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18
Q

Reciprocal translocation

A
  • Balanced translocation (no material lost or gained)
  • Can occur between any two chromosomes
  • Healthy - but infertility can occur (problems in pairing/segregation during meiosis)
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19
Q

Segregation types in reciprocal translocation + outcome of daughter cells

A

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

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20
Q

Examples of reciprocal translocations

A

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)

21
Q

Robertsonian translocation characteristics

A
  • 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)
22
Q

Acrocentric chromosomes

A
  • Chr 13, 14, 15, 21, 22

- NOR (nucleolar organizing region = repetitive rDNA)

23
Q

Inversions characteristics

A
  • 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
24
Q

Paracentric inversion

A

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

25
Q

Pericentric inversion

A

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)

26
Q

Ring chromosomes characteristics

A
  • Break removes both telomeres
  • Ends fuse together -> ring
  • Symptoms depend on extent of deletion
  • Mitotically stable
  • Replication (meiosis) often problematic
  • Partial monosomy in many
27
Q

Isochromosomes characteristics

A
  • 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
28
Q

Hemophilia A cause

A

Intrachromosomal rearrangement -> no factor VIII

29
Q

Numerical chromosome aberrations

A

Ploidy

  • Monosomy
  • Trisomy
  • Triploidy
30
Q

Euploidy

A

Normal number of structurally normal chromosomes (46)

31
Q

Aneuploidy definition+types

A

Less or more than the normal diploid number

  • Most frequent cytogenetic abnormality
    1) Monosomy
    2) Trisomy
32
Q

Monosomy characteristics

A
  • Lack of one of a pair of chromosomes
  • Turner syndrome (X0) - only viable monosomy
  • Due to non-disjunction in meiosis I or II
33
Q

Nondisjunction meiosis results + causes

A

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

34
Q

Trisomy characteristics

A

1 extra chromosome in a pair

  • Trisomy 13: Patau syndrome
  • Trisomy 18: Edward’s syndrome
  • Trisomy 21: Down syndrome
35
Q

Triploidy characteristics

A 
3 copies of EVERY chromosome (69 chromosomes)
Causes:
1) 2 sperms fertilize
2) Diploid sperm fertilize
3) Diploid ovum fertilized
Survivors are usually mosiac
36
Q

Down syndrome

A

Trisomy 21

  • Can also be caused by unbalanced Robertsonian translocation
  • Midpalmar crease often seen
37
Q

Sex chromosome abnormalities

A

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

38
Q

Uniparental disomy (UPD)

A

“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
39
Q

Mosaicism

A

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
40
Q

Chimera

A

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

41
Q

Microchimerism

A

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

42
Q

Preimplantation embryos

A

Higher number of chromosomal abnormalities

43
Q

Most common trisomy

A

Trisomy 16

*But lethal -> spontaneous abortion

44
Q

Spontaneous abortions

A
  • 50 % involve chromosomal abnormalities

- About 15 % of recognized pregnancies end in spontaneous abortion or miscarriage

45
Q

Clinical presentation suggestive of chromosomal abnormality

A

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

46
Q

Fluorochrome probes

A

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

47
Q

qh+

A

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

48
Q

Microdeletions/microduplications detection

A

Not detectable with banded karyotyping

- Must use FISH

49
Q

Burkitt lymphoma translocations

A

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

Genetics 2017 (19 decks)

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