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Year 2 EMS GiM > Cytogenetics - Inheritance > Flashcards

Cytogenetics - Inheritance Flashcards

1
Q

What is cytogenetics?

A

Study of chromosomes / anything bigger than a gene.

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2
Q

Which chromosomes are autosomes?

A

1-22.

23 = X/Y

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3
Q

Which chromosomes are acrocentric? (5)

A

13-15, 21, 22.

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4
Q

What is conventional cytogenetics?

A

Metaphase chromosome analysis.

-G banding

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5
Q

What is molecular cytogenetics?

A

Analysis at all stages of cell cycle.

not just metphase, like conventional

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6
Q

What are the main techniques of molecular cytogenetics?

A
  • FISH
  • Microarray CGH
  • Next generation sequencing
  • MLPA
  • QF-PCR
  • qPCR
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7
Q

At which stage of the cell cycle are chromosomes most visible?

A

Metaphase.

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8
Q

What is G-banding used for?

A

Karyotyping.

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9
Q

Which chromosome is generally the largest?

A

Chromosome 1.

-decrease in size from that

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10
Q

How many genes does each band contain?

A

~50.

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11
Q

What is the short arm of a chromosome called?

A

P.

-p1, p2

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12
Q

What is the long arm of a chromosome called?

A

Q.

q1, q2, q3

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13
Q

How do cytogenetic abnormalities produce an abnormal phenotype? (5)

A
  • Dosage effect (gain / loss)
  • Disrupt gene
  • Genomic imprinting
  • Position effect
  • Unmask recessive disorder
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14
Q

What generally produces a more severe phenotype; sex chromosome imbalance or autosomal?

A

Autosomal imbalance.

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15
Q

What are the main numerical chromosome abnormalities? (4)

A

Diploidy
Aneuploidy
Polyploidy
Mosaicism

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16
Q

What is diploidy?

A

2 copies of each chromosome.

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17
Q

What is aneuploidy?

A

Abnormal number of chromosomes in a cell.

  • gain (trisomy)
  • loss (monosomy)
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18
Q

What is polyploidy?

A

Gain of whole sets of chromosomes.

-triploidy / tetraploidy

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19
Q

What is mosaicism?

A

Presence of 2+ populations of cells.

-aneuploidy + diploidy

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20
Q

When do chromosomal abnormalities originate? (3)

A
  • Gametogenesis (meiosis)
  • Fertilsation
  • Early cleavage
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21
Q

What are the risks of increased maternal and paternal ages?

A

^ maternal age - aneuploidy.

^ paternal age - no significant risk.

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22
Q

What is non-disjunction?

A

Failure of chromosome / chromatid to separate.

23
Q

What are the different effects caused by non-disjunction at meiosis I and II?

A

Meiosis I - 2 disomic, 2 nullisomic gametes.

Meiosis II - 1 disomic, 1 nullisomic, 2 normal gametes

24
Q

What are the 3 chromosome that trisomy occurs at, and why?

A

13, 18, 21.

-relatively small chromosomes (can just about cope with extras)

25
Q

What proportion of foetuses with trisomy 21 spontaneously abort?

26
Q

What effect does trisomy 21 have on fertility?

A

Females - normal.

Males - usually infertile.

27
Q

What condition does trisomy 18 cause?

A

Edwards syndrome.

28
Q

What are the main features of Edwards syndrome?

A 
Microcephaly
Cleft lip
Low birth weight
Severe mental retardation
Heart problems
29
Q

What condition does trisomy 13 cause?

A

Patau syndrome.

30
Q

What are the main feature of Patau syndrome?

A 
Small birth weight
Microcephaly
Sloping forehead
Holoposencephaly 
Cleft lip
Polydactyly
31
Q

What is holoprosencephaly?

A

Forebrain fails to develop into two hemispheres.

32
Q

What age does female meiosis begin?

A

5 months.

  • the longer the eggs are unfertilised, the more likely they are damaged
  • male meiosis start at puberty
33
Q

What are the main sex chromosome aneuploidies? (2)

A 
Turner's syndrome (45, X)
Klinefelter syndrome (47, XXY)
34
Q

What are the main features of Turner’s syndrome?

A

Infertility
Lymph obstruction (webbed neck, swelling)
Short stature
Coarctation of aorta

35
Q

What are the main feature of Klinefelter syndrome?

A

Infertile
Hypogonadism
Long arm and legs

36
Q

What errors occur at fertilisation? (2)

A
  • Polyploidy (e.g. triploidy)

- Molar pregnancy (double paternal, no maternal)

37
Q

What is the genetic make up of trisomy, and what proportion spontaneously abort?

A

69, XXY / XYY / XXX.

-99.9% spontaneously abort

38
Q

What are the origin of triploidy? (3)

A
  • Digyny (diploid egg fertilised)
  • Diplospermy (diploid sperm)
  • Dispermy (2 sperm to one egg)
39
Q

What are the main features of double maternal triploidy?

A
  • Small placenta and foetus
  • Large head
  • Growth retardation
40
Q

What are the main features of double paternal triploidy?

A
  • Growth retardation

- Large, cystic placenta

41
Q

What are the conclusions from double maternal / paternal triploidy?

A

Maternal genome&raquo_space; foetus.

Paternal genome&raquo_space; placenta.

42
Q

What is a molar pregnancy?

A

Placenta develops without a foetus.

  • empty egg
  • double paternal genome&raquo_space; massive cystic placenta
43
Q

What errors occur at early cleavage?

A

Mosaicism.

-mitotic non-disjunction

44
Q

What are the main consequences of mosaicism?

A
  • Variable phenotype

- Recurrence risk (gonadal)

45
Q

Summarise numerical abnormalities.

A

MEIOSIS - gain / loss of single chromosomes.
FERTILISATION - gain of whole chromosome sets.
POST-FERTILISATION - gain / loss during mitosis.

46
Q

What are the 2 types of chromosomal rearrangements?

A

Balanced

Unbalanced

47
Q

What are the main types of balanced rearrangements? (3)

A
  • Translocation
  • Inversion
  • Insertion
48
Q

What are the 2 types of translocation?

A
  • Reciprocal (break and exhange)

- Robertsonian (whole arm fusion, no phenotype risk)

49
Q

Which type of translocation occurs with acrocentric chromosomes?

A

Robertsonian translocation.

50
Q

What is the process of inversion?

A

2 breaks, rotation, then rejoining.

- pericentric / paracentric

51
Q

What are unbalanced rearrangements?

A

Overall loss / gain of chromosomes.

  • commonest = deletions / duplications
  • mainly sporadic
52
Q

What is the difference between interstitial and terminal deletions?

A

INTERSTITIAL - middle of chromosome. 2 breaks&raquo_space; segment lost.
TERMINAL - end of chromosome. 1 break&raquo_space; segment lost.

53
Q

What are the 2 types of duplications?

A
  • Direct

- Inverted (segment reversed)

54
Q

What causes a ring chromosome?

A

Breakage then circularisation of a chromosome.

Year 2 EMS GiM (12 decks)

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