Chromosomal Chromosomal AberrationsAberrations

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DR.KIRTI SOLANKE

2Types of Chromosomes

Types of chromosomal aberrations/ abnormalities

NUMERICAL • ANEUPLOIDY• POLYPLOIDY

STRUCTURAL

• TranslocationsTranslocations• DeletionsDeletions• InsertionsInsertions• InversionsInversions• Rings, Rings,

IsochromosomesIsochromosomes• Different cell lines Different cell lines

(mixoploidy)(mixoploidy)• MosaicismMosaicism• ChimerismChimerism

Discuss mechanism of anomaly

Discuss mechanism of anomaly

Numerical Abnormalities

• Trisomy 21: Down’s Syndrome (47,XX + 21)• Trisomy 18: Edward’s Syndrome (47,XY + 18)• Trisomy 13: Patau’s Syndrome (47,XY + 13)• Trisomy of Sex Chromosome : Klinefelter

Syndrome (47, XXY)• Trisomy X: Triple X Syndrome (47, XXX)• Other Trisomies : Usually not viable.

• Monosomy X: Turner Syndrome (45, XO)• Autosomal Monosomies : Not viable

Trisomy 21; Down Syndrome

• over 60% of conceptions aborted spontaneously

• 20% stillborn• incidence increases sharply w/

maternal age• 1/300 for 35 year olds• 1/22 for 45 year olds

Causes-trisomy,translocation,mosaicism

Brushfield spots on iris

Hypotonia of muscles

Simian Crease

TURNER’S SYNDROME 45XO

• Causes:– Non-dysjunjtion

– Mosaicism

– Ring Chromosome

– Deletion

– Isochromosome

• Short stature• Widely spaced

nipples• Carrying angle at

elbow

Klinefelter's Syndrome (47, XXY)

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STRUCTURAL ABERRATIONSSTRUCTURAL ABERRATIONS

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Structural Abnormalities Of Structural Abnormalities Of ChromosomesChromosomes

• Result from the breaks in the chromosomesResult from the breaks in the chromosomes

• Causative factors for the breaks: Causative factors for the breaks: • Radiation, Drugs ,Viruses.Radiation, Drugs ,Viruses.

• Types of structural abnormalities are:Types of structural abnormalities are:

1.1. DeletionDeletion

2.2. InsertionInsertion

3.3. DuplicationDuplication

4.4. InversionInversion

5.5. IsochromosomeIsochromosome

6.6. TranslocationTranslocation

7.7. TranspositionTransposition

8.8. Ring ChromosomeRing Chromosome

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• Classified asClassified as– Stable & UnstableStable & Unstable

• Also classified asAlso classified as– Balanced & UnbalancedBalanced & Unbalanced

Structural Abnormalities Of ChromosomesStructural Abnormalities Of Chromosomes

23Terminal Deletion

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Interstitial Deletion

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Interstitial Deletion

Deletions• May arise through

unequal crossing over A B C D E F G

A B C D E F G

x

A B C D E F F G A B C D E G

Deletion Duplication

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INSERTION

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Insertion

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Insertion & Duplication

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INVERSION

Inversions

• Produced through breakage and reassociation of chromosome

A B

C

D

E

F G

Inversions

• Produced through breakage and reassociation of chromosome

A B

C

D

E

F G

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Pericentric Inversion

INVERSION

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Inversion: Pericentric & ParacentricInversion: Pericentric & Paracentric

Pericentric

35Paracentric

36INVERSION

Pericentric Inversion

Paracentric Inversion

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Isochromosome (Transverse centromeric

division)

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Isochromosome Isochromosome (Transverse centromeric division) (Transverse centromeric division)

Example:•Long arm of X- chromosome remains, short arms lost•Cytogenetic variant of Turner’s syndrome

39Isochromosome

40TRANSLOCATIONS

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Reciprocal Translocation video

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Robertsonian Translocation

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Acrocentric Chromosomes (Group D & G)

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Robertsonian Translocation:

Between two acrocentric chromosome e.g. Chromosome 13 & 21

Reciprocal (Balanced) translocation:

Between any two chromosomes Translocation

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Robertsonian Translocation

Common Robertsonian translocations are confined to the acrocentric chromosomes 13, 14, 15, 21 and 22; short arms of these chromosomes contain no essential genetic material.

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Ring Chromosome

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Ring ChromosomeRing Chromosome

e.g. r(22): Ring Chromosome no.22

STRUCTARAL ABERRATION