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Semester 1-MCBG > Session 16-Chromosome Abnormalities > Flashcards

Session 16-Chromosome Abnormalities Flashcards

1
Q

What is cytogenetics?

A

Study of genetic constitution of cells through the visualisation and analysis of chromosomes

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2
Q

Why do cytogenetic analysis? (4)

A
  1. Accurate diagnosis/prognosis of clinical problems
  2. Better clinical management
  3. Assess future reproductive risks
  4. Prenatal diagnosis
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3
Q

How many miscarriages counts as ‘recurrent foetal loss’?

A

3 or more

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4
Q

What are the two types of referral reasons?

A

Constitutional abnormalities

Acquired abnormalities

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5
Q

What are the types of constitutional abnormalities? (5)

A 
Prenatal diagnosis 
Birth defects
Abnormal sexual development 
Infertility 
Recurrent foetal loss
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6
Q

What are the types of acquired abnormalities? (3)

A
  1. Leukaemias:
    Acute disease-AML/ALL (acute myeloid/lymphoblastic leukaemia)
    Chronic disease-CML (chronic myeloid leukaemia)
    Myelodysplasia/myeloproliferative disorders
  2. Solid tumours
  3. Specific translocations/abnormalities
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7
Q

What are the two main methods of prenatal diagnosis?

A
  1. Chorionic villus sampling-at end of first trimester of pregnancy
  2. Amniocentesis-2nd trimester
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8
Q

Why do prenatal diagnosis? (5)

A
  1. Maternal serum screening for Down’s syndrome-blood sample taken at around 15 weeks, biochemical markers are measured
  2. First trimester screening
  3. FH chromosome abnormality
  4. Abnormal ultrasound scan
  5. DNA studies
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9
Q

What are some examples of birth defects? (5)

A
  1. Dysmorphism
  2. Congenital malformations
  3. Mental retardation
  4. Development delay
  5. Specific syndromes:
    Down syndrome (trisomy 21)
    Williams syndrome
    DiGeorge syndrome
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10
Q

What is karyotyping?

A

Systemic sorting of chromosomes

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11
Q

What is aneuploidy?

A

Loss and gain of whole chromosomes due to errors at cell division in meiosis

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12
Q

Give three examples of trisomies

A

Down Syndrome +21
Patau syndrome +13
Edwards +18

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13
Q

Give an example of a monosomy

A

Turner syndrome 45,X (X inactivation)

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14
Q

What is polyploidy?

A

Gain of a whole haploid set of chromosomes

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15
Q

What is the cause of polyploidy?

A

Polyspermy=fertilisation of an egg by more than one sperm

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16
Q

What are the causes of aneuploidy?

A

Originates from non-disjunction at one of the meiotic cell divisions and forms gametes with a missing chromosome and an extra chromosome

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17
Q

True or false: aneuploidy can occur during mitotic cell division

A

TRUE

18
Q

What does aneuploidy in mitotic cell division cause?

A

Mosaicism ie two cell populations in an individual

19
Q

What are the characteristics of Down syndrome? (6)

A 
Hypotonia
Characteristic facial features
Intellectual disability 
Heart defects
Increased prevalence of leukaemia 
Increased incidence of early Alzheimer's
20
Q

What are some of the signs of Edwards syndrome? (4)

A

Small lower jaw
Low-set ears
Rocker bottom feet
Overlapping fingers

21
Q

What is X chromosome inactivation?

A

Only one X chromosome is ever active in a human cell

22
Q

Why is a single X chromosome a problem?

A

X and Y chromosomes have short regions in common at the tips of the long and short arms (PAR1 in Y and PAR2 in X) and this allows for pairing during cell division. Turner syndrome patients will be monosomic for genes in the PARs

23
Q

Which gene is associated with short stature?

A

SHOX (within PAR)

24
Q

What are the signs of Turner syndrome? (6)

A 
Puffy feet
Redundant skin at back of neck
Short stature
Heart defects 
Mild learning difficulties 
Infertility
25
Q

What is mosaicism?

A

Presence of two or more cell lines in an individual

26
Q

What are the two types of translocations?

A

Reciprocal

Robertsonian

27
Q

What are the different types of cytogenetic structural abnormalities? (8)

A 
Translocations
Inversions
Deletions
Duplications 
Insertions 
Rings
Marker chromosomes 
Isochromosomes
28
Q

What are isochromosomes?

A

Mirror image chromosomes

29
Q

What are the two types of inversions?

A

Paracentric

Pericentric

30
Q

What are reciprocal translocations?

A

Two break rearrangements - exchange of material between nonhomologous chromosomes

31
Q

What are the types of mal-segregation in meiosis?

A

Adjacent 1-non homologous centromeres move together to daughter cell
Adjacent 2-homologous centromeres
3:1 non disjunction
4:0 non disjunction

32
Q

What does FISH stand for and what is it?

A

Fluorescent in situ hybridisation

Molecular cytogenetic technique

33
Q

What are the different types of FISH probes? (4)

A
  1. Locus/gene specific probes
  2. Centromere probes
  3. Telomere probes
  4. Whole chromosome paints
34
Q

What are centromere probes used for and what are their characteristics?

A

Large probes, easy to see metaphase and interphase

Used for: identifying derivative chromosomes and markers

35
Q

What are whole chromosome paints used for?

A

To identify individual chromosomes even when they are rearranged

36
Q

What are locus specific probes used for?

A

Microdeletion/duplication syndromes

37
Q

What does microarray comparative genomic hybridisation (aCGH) examine?

A

Whole genome at high resolution

38
Q

What are the advantages of aCGH? (5)

A
  1. Examines entire genome and high resolution
  2. Targeted against known genetic conditions
  3. One array is equivalent of many FISH investigations
  4. Detailed info on genes in del/dup region
  5. Better phenotype/genotype correlation
39
Q

What are the disadvantages of aCGH? (4)

A
  1. Arrays more expensive than karyotyping
  2. Won’t detect balanced rearrangements
  3. Copy number variation
  4. Mosaicism may be missed
40
Q

What is copy number variation?

A

Sections of genome are repeated and number of repeats in genome vary between individuals

Semester 1-MCBG (20 decks)

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