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

Chromosomal Abnormalities & Analysis Flashcards

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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?

A
  • POLYSPERMY

- Fertilisation of an oocyte by more than one sperm cell

25
Q

How is aneuploidy caused?

A

NON-DISJUNCTION AT ONE OF THE MEIOTIC CELL DIVISIONS where both chromosomes go into one daughter cell

26
Q

What does aneuploidy cause in mitosis?

A

MOSAICISM

27
Q

Define mosaicism

A
  • 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
Q

What is the karyotype for a female with Down’s syndrome?

A

47,XX+21

29
Q

What is the karyotype for Turner’s syndrome?

A

45,X

30
Q

What is anaphase lag?

A

Chromosomes are left behind during separation due to DEFECTS IN SPINDLE FUNCTION OR ATTACHMENT TO CHROMOSOMES

31
Q

How is Edwards syndrome caused?

A

Trisomy 18

32
Q

What does trisomy 13 cause?

A

Patau Syndrome

33
Q

What is the role of X chromosome inactivation?

A

Ensures that humans have the same active X chromosome (only 1 X chromosome is active)

34
Q

What is uniparental disomy UPD?

A

Presence of homologous chromosomes from one parent

35
Q

What is the difference between heterodisomy and isodisomy?

A
  • HETERODISOMY is where you gain 2 homologous chromosomes from one parent
  • ISODISOMY is where you get 2 identical chromosomes from one parent
36
Q

What is segmental UPD?

A

Only part of a chromosome is involved in uniparental disomy

37
Q

What is the significance of UPD?

A
  • 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
Q

Which chromosomes can UPD syndromes arise from?

A

6,7,11,14,15,16

39
Q

How does trisomy rescue occur?

A
  • 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
Q

How does UPD occur?

A

TRISOMY RESCUE

41
Q

What is a reciprocal translocation?

A
  • 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
Q

What segregation types will give an unbalanced chromosome?

A
  • ADJACENT 1 non homologous centromeres

- ADJACENT 2 homologous centromeres

43
Q

How does robertsonian translocation occur?

A
  • FUSION OF 2 ACROCENTRIC CHROMOSOMES (13,14,15,21,22)
  • Can be mono or dicentric
  • CHROMOSOME COUNT OF 45 IS BALANCED
44
Q

What is the abbreviation for a Robertsonian translocation?

A

Der

45
Q

What does a karyotype of der(14;21) mean?

A

Robertsonian S translocation between chromosomes 14 and 21

46
Q

What technique is used to view microdeletions on chromosomes?

A

Fluorescent in situ hybridisation (FISH)

47
Q

How do deletions occur on chromosomes?

A
  • UNEVEN PAIRING AND RECOMBINATION DURING MEIOSIS

- Can be TERMINAL (on end of arms) or INTERSTITIAL (within arms)

48
Q

What can FISH be used for?

A
  • Identifying microdeletions
  • Identifying chromosomes by centromeres
  • Identifying telomeres (terminal deletions)
  • WHOLE CHROMOSOME PAINTING
49
Q

What is the purpose of whole chromosome painting?

A

Identify chromosome in a rearrangement

50
Q

What are centromere probes used for?

A

Copy number analysis

51
Q

What is microarray used for?

A
  • COPY NUMBER CHANGES

- Examines the whole genome at a high resolution

52
Q

Describe the process of microarray

A
  • 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
Q

What are the disadvantages of using microarray?

A
  • EXPENSIVE
  • Will not detect balanced arrangements
  • Mosaicism may be missed
  • COPY NUMBER VARIATION
54
Q

What is non invasive prenatal testing NITP?

A

Obtaining foetal DNA from maternal blood at 9 weeks gestation

55
Q

What is ISCN?

A

International system of Cytogenic nomenclature

56
Q

What methods could a UPD originate from?

A
  • TRISOMY RESCUE
  • MONOSOMY RESCUE
  • GAMETE COMPLEMENTATION
  • MITOTIC ERROR
57
Q

How can mosaicism occur?

A
  • Mitotic (post-zygotic) non disjunction event

- Anaphase lag

58
Q

What is Klinefelters syndrome and how does it occur?

A
  • 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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