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302: Scientific basis of medicine > Chromosomal abnormality > Flashcards

Chromosomal abnormality Flashcards

1
Q

Chromosomal functions (2)

A

Genetic inheritance

Stabilises cellular DNA

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2
Q

Function of:

  • Telomere
  • Centromere
A

Telomere
- Protects ends

Centromere

  • Holds chromatids together
  • Segregates chromosomes
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3
Q

Chromosome classification (in relation to centromere:

  • metacentric
  • sub-metacentric
  • acrocentric
A

Metacentric= middle

sub-metacentric= close to one telomere

Acrocentric= centromere near telomere.

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4
Q

Human karyotype

- Chromosome sets

A

2 haploid sets of 23

- 44 autosome, 2 sex chromosomes

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5
Q

Aneuploidy

A

Incorrect number of chromosomes (too many or few)

  • Gametes can be generated via mitotic nondisjunction
  • Most common cause= maternal meiosis
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6
Q

Balanced and unbalanced rearrangements

A

Balanced= translocation, inversions

Unbalanced= deletions, duplications

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7
Q

Nondisjunction

A

Failure of homologous chromosomes/ sister chromatids to separate during cell division

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8
Q

Post-zygotic nondisjunction and mosaicism

A

If post-zygotic, can lead to mosaicism

Can also occur in trisomic concepts and lead to anaphase lag

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9
Q

Anaphase lag

A

Sister chromatids to not separate properly.

  • Due to spindle problems
  • Leads to loss chromsome
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10
Q

Down’s syndrome

- Features

A

Most common autosomal abnormality

Presents

  • Learning difficulties
  • Dysmorphic features
  • Heart defects
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11
Q

Down’s syndrome

- Karyotypes

A

Main= primary trisomy
- 47, XX + 21

1-2% mosicism= 46, XX/ 47 XX = 21

4%= translocation
der (14; 21)

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12
Q

Edward’s syndrome

  • Defect
  • Features
A

Trisomy 18

Features

  • Dysmorphic
  • Rocker bottom feet
  • Congenital heat defects
  • Die within weeks

Karyotype

  • +18.
  • 5% mosaicism
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13
Q

Patau’s syndrome

  • Defect
  • Features
A

Trisomy 13

Dysmorphic features
Renal abnormalities, cardiac defects

Most die within a year

Karyotype

  • primary trisomy
  • 20% translocation (13;14)
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14
Q

Klinerfelter syndrome

  • Genetic defect
  • Features
A

XXY

Features

  • Tall
  • Gynaecomastia
  • Small tests
  • Infertility
  • Delayed/ incomplete puberty

Karyotype

  • XXY
  • Mosaicism XXY/ XY
  • XXXY XXXXY
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15
Q

Turner syndrome

  • Genetic defect
  • Features
A

XO

Features

  • Short
  • infertile
  • Maternal age NOT risk factor

Karyotype

  • 40-60% monsomy
  • Moasicism
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16
Q

XYY syndrome

A

Often asymptomatic

Features may include

  • Learning disabilities
  • Speech delay
  • Hypotonia

Karyotype
- XXY, or mosaicism (XY)

17
Q

Triple XXX syndrome

A

Mainly asymptomatic
- seizures and kidney abnormalities

XXX or mosaicism with XX

18
Q

Lyonisation

A

Random activation of X chromosome in females
- Leads to less severity of sex chromosomal disorders.

Mechanism

  • 2 weeks post-fertilisation
  • Only one active X
19
Q

X-inactivation mechanism

A

Occurs in X inactivation centre (XIC)

Xist (transcript RNa)

  • expressed on inactive X
  • Transcripts coat the X chromosome and lead to inactivation
20
Q

Chromosomal translocations

- Definition

A

Rearrangement of chromosome segment transferred to non homologous chromosome or new site on same chromosome

21
Q

Robertsonian translocation

A

Fusion of two acrocentric chromosomes
- Commonly 13;14 or 14;21

Phenotype is normal in balanced carriers but there is reproductive risks

22
Q

Translocation down’s

A

fusion of long arms of chromsome 14 and chr 21

carrier= 46 xx, -14, -21 +t(14q21q)

downs= t(14;21) 21

23
Q

Reciprocal translocation

A

two way exchange between non-homologous

  • If balanced= normal
  • Carrier= reproductive risks
24
Q

isochromosome

A

Occurs from centromere fission

- where one arm is deleted, the other replicated

25
Q

ring chromosome

A

when telomeric region is lost and the arms fuse

26
Q

duplication

A

> 1 copy of chromosome segment

27
Q

cru du chat

A

Genetic condition due to deletion on chr 5p

302: Scientific basis of medicine (28 decks)

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