Lecture 2b - Numerical Chromsome Aberrations Flashcards

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1
Q

Euploidy

A

-normal number of structurally normal chrs

euploid females have 46 chrs - 44 autosomes, 2 X

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2
Q

Aneuploidy

A
  • less or more than normal diploid number

- recognized as small deviation -> major deviations are not compatible with lfie

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3
Q

Most common Aneuploidies

A

1) Monosomy:
- lack of one pair of chromosomes
- usually lethal (X monosomy quite common)

2) Trisomy:
- eg/ Downsyndrome (Trisomy 21)
- additional copy of a chromosome
- incidence of trisomy incr withmaternal age

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4
Q

Pathways which generate Aneuploidy

A

1) Mitotic Checkpoint defect
2) Cohesion defect
3) Merotelic attachment
4) Multipolar mitotic division

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5
Q

Common cause of Trisomy

A

Meiotic Non-Disjunction
1 = All zygotes are abnormal (2x monosomic, 2x trisomic)
2= 50% Euploid, 25% Monosomic, 25% trisomic

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6
Q

Down syndrome

A
  • 95% of cases = Trisomy 21 (47 XY + 21)-> cause meiotic non-disjnxn
  • Parents have normal Karyotype
  • Maternal age -> indic meiotic non dij in Ovum (95% of cases extra Chrs from mother)
  • Paternal Age - no corell (but can in rar cases come from)
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7
Q

Other causes of Downsyndrome

A

-4% - T(14,12) Robertsonian Trnaslocation -> long arm of Chrs not whole chrs

-1% MOSAICS:
> hve 46 and 47 in cells -> MITOTIC NON-Disjunction in early embryogenesis

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8
Q

Other Trisomy

A

1) PATAU Syndrome: 13

2) EDWARDS SYNDROME: 18

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9
Q

Triploidy

A
  • three of every chromosomes
  • 69 chrs (3 haploid sets of 23)
  • rare and such individuals very abnormal –> survivors are mosaic (some cells 46 some 69)
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10
Q

Cause of Triploidy

A
  • Fertilization by 2 sperms

- Fertilization by Diploid Sperm/Ovum

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11
Q

Sex Chromosome Abnormalities

A
  • Xo = TUrners (45, X0)
  • XXY: Klienfelter
  • XXX: Super WOman
  • XYY Jacobs (low inteligence - tall - criminals)
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12
Q

Uni-parental Disomy (UPD)

A

-both chrs in a zygote come from a single parent

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13
Q

Trisomic Rescue (Uniparental rescue)

A
  • Fertilized egg = trisomy due non-disjunction

- a copy is lost from trisomy to form normal number –> if remaining copies from same parent = UPD

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14
Q

Somatic Duplication (Monosomic Rescue)

A
  • fertilized ovum has 1 chrs from normal parent + no chrom from other (NULLISOMY)
  • monosomy overcome by -> somatic Duplication –> UPD
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15
Q

UPD clinically

A
  • Prader-willi + Angelmann
  • involve 15q

other defects:
> Imprinting defects
> Microdeletion (15q)

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16
Q

Mosaic

A
  • individual with more than 1 cytogenetically distinct populations of cells with same origin
  • usually people with turner syndrome -> are Mosaics
17
Q

X-chromosome Mosaicism

A
  • X-inactivation occurs randomly

- half cells have paternal/maternal X inactive

18
Q

Chimera

A

-ptnt has more than one cytogenetically distinct population of cells with different origin

19
Q

Example of Chimera

A

-Pregnancy leads to Microchimerism:

> presence of small number of cells that originate from another individual