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Practical 7 07

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  • 1. Practical 7 Numerical chromosomal abnormalities – conclusion
  • 2. Nondisjunction of sex chromosomes during spermatogenesis – 1 st meiotic division XY XY XY XY XXY XXY X X +X nondisjunction fertilization
  • 3. Nondisjunction of sex chromosomes during spermatogenesis – 2 nd meiotic division – X chromosome XY Y X XX Y Y XXX X XY XY +X nondisjunction fertilization
  • 4. Nondisjunction of sex chromosomes during spermatogenesis – 2 nd meiotic division – Y chromosome XY Y X X X YY XX XX XYY X +X nondisjunction fertilization
  • 5. 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
  • 6. Task 1 : Describe following karyotype according to ISCN1995. How much Barr bodies are present in somatic cells of this individual?
    • 49,XXXXY
    • Rare form of Klinefelter syndrome
    • 3 Barr bodies
    Number of Barr bodies = X chromosome number – 1
  • 7. Practical 7 Structural chromosomal abnormalities
  • 8. Task 2 : The photo 1 shows multiple structural abnormalities after irradiation of an individual with high dosage of X-rays. Describe structural chromosomal aberrations on the photo. Photo 1 gap breakage triradial quadriradial chromatid breakage chromosomal (double-chromatid) breakage
  • 9. Origin of structural chromosomal abnormalities
    • Incorrect repair of chromosomal breakages – mainly interchromosomal rearrangements
    • Non-reciprocal crossing-over during meiosis I. – intrachromosomal rearrangements – microdeletion syndromes, X;Y translocation
  • 10. Task 3
    • A boy (see photo) with severe mental retardation had been cytogenetically examined – see karyotype.
    • Describe corresponding chromosomal abnormality and determine the cytogenetic finding.
    Karyotype 3
  • 11. Terminal deletion of short arms of the chromosome 5 46,XY,del(5)(p15.2) Simplified finding: 46,XY,del(5p)
  • 12. Cat cry syndrome Cri du chat syndrome
    • A disorder caused by the loss of part of the short (p) arm from chromosome 5. Also called the cri du chat (or cri-du-chat) syndrome.
    • incidence varies between 1 in 20,000 to 1 in 50,000 births.
    • The frequency of the syndrome among profoundly retarded patients (with an IQ less than 20) is approximately 1 in 100.
    • severe developmental and mental retardation ( IQ below 20)
    • characteristic constellation of congenital malformations:
      • microcephaly (small head)
      • round face
      • hypertelorism (wide-spread eyes)
      • micrognathia (small chin)
      • epicanthal folds (inner eye folds)
      • low-set ears
      • hypotonia (poor muscle tone)
      • some patients survive into adulthood
  • 13. Task 4
    • A child with the Down syndrome had been cytogenetically examined. The mother and the father are healthy.
    • Describe the chromosomal abnormality in the child and put down the cytogenetic finding .
    • Calculate the risk for further offspring of the mother.
    Photo – karyotype 4
  • 14. Robertsonic translocation of chromosomes 14 and 21 Down syndrome – translocation form der(14;21)
  • 15. Robertsonic translocation = robertsonic fusion = centric fusion Translocation of two acrocentric chromosomes, centromeric fusion. derivative chromosome
  • 16. 46,XY,der(14;21)(q10;q10),+21 older description : 46,XY,t(14;21)
  • 17. For calculation of the risk for further offspring karyotyping of parents is necessary.
  • 18. Karyotype of the mother balanced robertsonic translocation of chromosomes 14 and 21 Photo – karyotype 5
  • 19. 45,XX,der(14;21)(q10;q10) older description: 45,XX,t(14;21)
  • 20. The mother is carrier of balanced robertsonic translocation of chromosomes 14 and 21. She is healthy but her offspring has increased risk of the Down syndrome.
  • 21. Risk for further offspring Normal karyotype Carrier M. Down Trisomy 14 Monosomy 21 Monosomy 14 Lethal during prenatal development Theoretical risk 1/3 … 33% Empiric risk 8 – 10% Chromosomal constitution of mother carrier:
  • 22. Task 5
    • A child with the Down syndrome had been cytogenetically examined. The mother and the father are healthy.
    • Describe the chromosomal abnormality in the child and put down the cytogenetic finding.
    • Calculate the risk for further offspring of the mother.
    Photo 6 – karyotype of the child
  • 23. Robersonic translocation of two 21 chromosomes Translocation form of the Down syndrome der(21;21)
  • 24. 46,XY,der(21;21)(q10;q10),+21 older description : 46,XY,t(21;21) der(21;21)
  • 25. Karyotype of the mother balanced robertsonic translocation of two 21 chromosomes Photo (karyotype) 7 der(21;21)
  • 26. 45,XX,der(21;21)(q10;q10) older description: 45,XX,t(21;21) der(21;21)
  • 27. Risk for further offspring der(21;21) Risk: 100% +21 fertilization der(21;21) nulisomic gamete m. Down monosomy 21 – lethal during early prenatal development
  • 28. Task 6 A girl with a Turner syndrome features had been examined in the genetic counselling clinic. Describe her karyotype and determine the chromosomal finding.
  • 29. Isochromosome of long arm of chromosome X 46,X,i(X)(q10) older description: 46,X,iso(Xq)
  • 30. Origin of isochromosomes i(Xp) i(Xq) Normal separation in anaphase Abnormal division – origin of i s ochromosomes Xp and Xq
  • 31. Chromosomal abnormalities in Turner syndrome:
    • Numerical aberrations:
      • X m onosomy : 45,X
      • X m onosomy in mosaic: 45,X/46,XX
    • Structural aberrations:
      • Isochromosome Xq, isochromosome Xp
      • Deletion forms: „46,X,del(Xp)“, „46,Xdel(Xq)“
      • Ring chromosomes: 46,X,r(X)
  • 32. Origin of ring chromosome reparation deletion of terminal segments ring chromosome r(X)
  • 33. Task 7
    • A boy (see photo) with mental retardation , long narrow face, large ears, a high arched palate, flat feet and overly flexible joints (especially the fingers) had been cytogenetically examined. The karyotype contained abnormality on chromosome X – see partial karyotype.
    • Describe X- chromosomal abnormality and determine the cytogenetic finding.
    Photo 2 – partial karyotype of chromosome X
  • 34. Fragile site on band Xq27.3
    • 46,Y,fra(Xq27.3)
    • Gene responsible for fragile X syndrome is called FMR1 (fragile X mental retardation 1).
    • The gene appears in three forms that are defined by the number of repeats of a pattern of DNA called CGG repeats:
      • Individuals with less than 60 CGG repeats have a normal gene.
      • Individuals with 60 – 200 CGG repeats have a premutation ( they carry an unstable mutation which can expand in future generations ) .
      • Individuals with over 200 repeats have a full mutation which causes fragile X syndrome. The full mutation causes the gene to shut down or methylate a region of the FMR-1 gene.
    • Normally, the FMR-1 gene produces an important protein called FMRP. When the gene is turned off, the individual does not make fragile X mental retardation protein (FMRP).  The lack of this specific protein causes fragile X syndrome .
  • 35. Fragile X syndrome
    • the most common inherited cause of mental impairment.
    • The syndrome occurs in approximately 1 in 3600 males.
    • the most common cause of inherited mental impairment. This impairment can range from learning disabilities to more severe cognitive or intellectual disabilities.
    • the most common known cause of autism or "autistic-like" behaviors.
  • 36. See you at the end of the summer term!