practical 6 07

Practical 6

Numerical chromosomalabnormalities

Task A• A fetus with multiple

malformations including

syndactyly had been

cytogenetically

examined

• Determine and describe

the chromosomal

finding.

Triploidy 69,XXY

Lethal during prenatal development.

Partial hydatidiform mole

Mass of trophoblastic tissue

Mosaic form of triploidy

69,XXY/46,XY

69,XXX/46,XX

Numerical chromosomal abnormalities

• Polyploidy– Triploidy 3n– Tetraploidy 4n

• Aneuploidy– in somatic cells

• Trisomy 2n+1• Monosomy 2n – 1• Tetrasomy 2n + 2

– in gametes• Nullisomy n – 1• Disomy n + 1

Normal karyotype

Triploidy

Trisomy

Monosomy

Aneuploidy

Polyploidy

Task 1

• Determine the chromosomal finding.

• Karyotype 1

Trisomy 21

47,XX,+21

47,XY,+21

Down syndrome

47,XX,+21

47,XY,+21

Down syndrome

Down syndrome

Epicanthic fold Palm or „simian“ crease

Phenotypic features of the Down syndrome

Trisomy 21 in the fetus

Cause of chromosomal aneuploidies – non-disjunction

• Meiotic

• Mitotic

leads to mosaic

Task 3

• Determine following karyotypes and

describe corresponding phenotypic

features

• See karyotypes 2, 3, 4, 5, 6, 7

Karyotype 2

Trisomy of chromosome 13

47,XX,+13

Patau syndrome

Patau syndrome

polydactyly

Patau syndrome – cyclopia

Karyotype 3

Trisomy of chromosome 18

47,XY,+18

Edwards syndrome

Trisomy 18

Edwards syndrome

Edwards syndrome

„rocker bottom feet“

A fetus with trisomy 18

Fetus with trisomy 18

Karyotype 4

Monosomy of chromosome X

45,X

Turner syndrome(Ulrich-Turner syndrome)

Turner syndrome – streak gonads

Phenotypic features of the Turner syndrome

Monosomy X in the fetus

• Very frequent abnormality in

miscarriages

• It is possible that full

monosomy is lethal during

prenatal development

• Only mosaic forms can

survive?

Description of the mosaic form of the Turner syndrome

• 45,X [40] / 46,XX [35]

• 40 + 35 = 75 cells had been examined

• In 40 cells monosomy X was identified.

• 35 cells had normal karyotype.

Karyotype 5

47,XXY

Klinefelter syndrome

Phenotypic features of the Klinefelter syndrome

Klinefelter syndrome phenotype

Karyotype 6

Superfemale – 47,XXX

Karyotype 7

Supermale – 47,XYY

Barr body examination

Epithelial cells from the buccal smear

Barr body

• = sex-chromatin

• Inactivated X chromosome

• Female XX

– 1 Barr body

• Male XY

– no Barr hody

• Klinefelter syndrome XXY

– 1 Barr body

Murray L. Barr

Task 4

• Estimate possible constitution of

sex chromosomes in an

individual with two Barr bodies.

Possible chromosomal findings:

Superfemale – 47,XXX

Rare form of the Klinefelter syndrome – 48,XXXY

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