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ESA1 - Molecules, Genes And Disease > Chromosomal Abnormalities & Analysis > Flashcards

Chromosomal Abnormalities & Analysis Flashcards

(58 cards)

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1
Q

What is a karyotype?

A

Picture of the full set of stained metaphase chromosomes of an individual, organised by chromosome number

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2
Q

Describe the features of chromosome painting

A
  • Automated, using a computer

- Each chromosome is visualised using a different coloured fluorescent probe

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3
Q

Describe the process of fluorescent in situ hybridisation (FISH)

A
  • Investigation of DNA sequence of chromosomes INSIDE cells
  • Hybridisation of a fluorescent labelled probe
  • Can detect DNA sequences at specific locations on chromosomes e.g. telomeres (ends) and centromeres
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4
Q

When are chromosomes harvested for analysis?

A

During METAPHASE

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5
Q

What is a metacentric chromosome?

A

Chromosome where the p and q arms are the same length

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6
Q

What are the main chromosome morphologies?

A
  • Metacentric (p and q arms are the same length)
  • Submetacentric (p arm is smaller than q arm)
  • Acrocentric (very small p arm)
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7
Q

Which groups of chromosomes are acrocentric?

A

D and G

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8
Q

How are chromosomes G stained?

A
  • Metaphase chromosomes exposed to trypsin which digests proteins
  • Stained with ROMANOWSKI type dye
  • BANDING PATTERN where AT rich areas stain DARK and CG apricot areas stain LIGHT
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9
Q

Why do chromosomes demonstrate a banding pattern?

A
  • A-T rich areas stain DARK

- C-G rich areas stain LIGHT

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10
Q

Which areas of the chromosomes are gene rich?

A

LIGHT staining C-G

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11
Q

What is C banding?

A

Staining of HETEROCHROMATIN at centromeres and 1, 9, 16 Yq chromosomes

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12
Q

What is the karyotype for a normal female?

A

46,XX

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13
Q

What are the benefits of analysing chromosomes?

A
  • Accurate diagnosis and prognosis of clinical problems
  • Better clinical management (e.g. Hormonal treatment)
  • Assess future reproductive risks
  • Pre-natal diagnosis
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14
Q

Why might someone be referred for chromosomal analysis?

A
  • Abnormal sexual development
  • Prenatal diagnosis
  • Birth defects
  • Acquired abnormalities e.g. Acute or chronic diseases
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15
Q

Name 2 methods than can be used for extracting foetal DNA for pre natal diagnosis

A
  • Amniocentesis

- Chorionic villus biopsy

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16
Q

Why might someone want a pre-natal diagnosis?

A
  • Test for presence of birth defects e.g. DOWNS SYNDROME

- Family history of chromosomal abnormalities

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17
Q

What is aneuploidy?

A

LOSS OR GAIN OF WHOLE CHROMOSOMES

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18
Q

How does aneuploidy occur?

A

Errors at cell division in meiosis

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19
Q

What is Down’s syndrome an example of? (Hint: +21)

A

TRISOMY

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20
Q

Define trisomy and give an example

A
  • Type of aneuploidy where there are 3 copies of a particular chromosome instead of 2
  • DOWNS SYNDROME has an extra chromosome 21
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21
Q

What is monosomy? Give an example of a disease in which this occurs

A
  • Only have one copy of a chromosome from a chromosome pair

- e.g. TURNERS SYNDROME where there is only one X chromosome (only affects girls)

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22
Q

What is polyploidy?

A

GAIN OF A WHOLE HAPLOID SET OF CHROMOSOMES

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23
Q

What are the possible karyotypes of a triploidy?

A
  • 69 XXX
  • 69 XXY
  • 69 XYY
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24
Q

How does polyploidy occur?

Study These Flashcards
A
  • POLYSPERMY

- Fertilisation of an oocyte by more than one sperm cell

25
How is aneuploidy caused?
NON-DISJUNCTION AT ONE OF THE MEIOTIC CELL DIVISIONS where both chromosomes go into one daughter cell
26
What does aneuploidy cause in mitosis?
MOSAICISM
27
Define mosaicism
- Presence of 2 OR MORE CELL LINES in an individual - Due to non-disjunction in mitosis - Can occur in EARLY or LATE cell divisions
28
What is the karyotype for a female with Down's syndrome?
47,XX+21
29
What is the karyotype for Turner's syndrome?
45,X
30
What is anaphase lag?
Chromosomes are left behind during separation due to DEFECTS IN SPINDLE FUNCTION OR ATTACHMENT TO CHROMOSOMES
31
How is Edwards syndrome caused?
Trisomy 18
32
What does trisomy 13 cause?
Patau Syndrome
33
What is the role of X chromosome inactivation?
Ensures that humans have the same active X chromosome (only 1 X chromosome is active)
34
What is uniparental disomy UPD?
Presence of homologous chromosomes from one parent
35
What is the difference between heterodisomy and isodisomy?
- HETERODISOMY is where you gain 2 homologous chromosomes from one parent - ISODISOMY is where you get 2 identical chromosomes from one parent
36
What is segmental UPD?
Only part of a chromosome is involved in uniparental disomy
37
What is the significance of UPD?
- IMPRINTING - If the chromosome involved is not imprinted there will be NO phenotypic effect - Imprinted chromosomes show differential gene expression depending on parental origin
38
Which chromosomes can UPD syndromes arise from?
6,7,11,14,15,16
39
How does trisomy rescue occur?
- NON-DISJUNCTION IN MEIOSIS to produce a trisomy haploid cell - NON-DISJUNCTION IN MITOSIS of the trisomy cell to produce a disomy cell (normal)
40
How does UPD occur?
TRISOMY RESCUE
41
What is a reciprocal translocation?
- TWO BREAK REARRAGEMENTS where part of a chromosome is lost and attaches to another (usually within the same family) but t(11;22) is an exception - Can produce BALANCED (alternate) or UNBALANCED (adjacent 1/2) gametes
42
What segregation types will give an unbalanced chromosome?
- ADJACENT 1 non homologous centromeres | - ADJACENT 2 homologous centromeres
43
How does robertsonian translocation occur?
- FUSION OF 2 ACROCENTRIC CHROMOSOMES (13,14,15,21,22) - Can be mono or dicentric - CHROMOSOME COUNT OF 45 IS BALANCED
44
What is the abbreviation for a Robertsonian translocation?
Der
45
What does a karyotype of der(14;21) mean?
Robertsonian S translocation between chromosomes 14 and 21
46
What technique is used to view microdeletions on chromosomes?
Fluorescent in situ hybridisation (FISH)
47
How do deletions occur on chromosomes?
- UNEVEN PAIRING AND RECOMBINATION DURING MEIOSIS | - Can be TERMINAL (on end of arms) or INTERSTITIAL (within arms)
48
What can FISH be used for?
- Identifying microdeletions - Identifying chromosomes by centromeres - Identifying telomeres (terminal deletions) - WHOLE CHROMOSOME PAINTING
49
What is the purpose of whole chromosome painting?
Identify chromosome in a rearrangement
50
What are centromere probes used for?
Copy number analysis
51
What is microarray used for?
- COPY NUMBER CHANGES | - Examines the whole genome at a high resolution
52
Describe the process of microarray
- Take samples of patient DNA and control DNA - Mark each one with a probe (patient DNA is GREEN and control DNA is RED) - Excess GREEN indicates DUPLICATION of test DNA - Excess RED indicates DELETION of test DNA
53
What are the disadvantages of using microarray?
- EXPENSIVE - Will not detect balanced arrangements - Mosaicism may be missed - COPY NUMBER VARIATION
54
What is non invasive prenatal testing NITP?
Obtaining foetal DNA from maternal blood at 9 weeks gestation
55
What is ISCN?
International system of Cytogenic nomenclature
56
What methods could a UPD originate from?
- TRISOMY RESCUE - MONOSOMY RESCUE - GAMETE COMPLEMENTATION - MITOTIC ERROR
57
How can mosaicism occur?
- Mitotic (post-zygotic) non disjunction event | - Anaphase lag
58
What is Klinefelters syndrome and how does it occur?
- Genotyoe 47XXY whereby the male has an extra copy of the X chromosome - Caused by NON DISJUNCTION event in meiosis of either parent, forming a trisomy cell XY - Individual would display female characteristics in phenotype and would be infertile

ESA1 - Molecules, Genes And Disease (16 decks)

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