Chromosomal abnormalities

• Chromosomal abnormalities

  Deviations from the normal chromosome number or structure
• Cytogenetics

  The study of the structure and function of chromosomes
• Karyotype

  A preparation of chromosomes arranged in size order
• How are chromosomes identified

  
  

  • Length
  • Banding pattern
  • Placement of centromere
• How is the banding pattern on a chromosome visualized

  With a giemsa stain.
• Karyotyping used for

  • A. to detect changes in chromosome number
  • B. to detect changes in chromosome structure
• Polyploidy

  Extra whole sets of chromosomes
• Polyploidy

  • Triploid = 3n
  • Tetraploid = 4n
• Aneuploidy

  Some additional or missing chromosomes
• Monosomy

  One chromosome missing
• Trisomy

  One extra chromosome
• Write the karyotipe for trisomy 18

  47,XX,+18
• What is Non-disjunction

  When the chromosomes fail to separate
• Autosomal aneuploidy that permits survival into adulthood

  Down's Syndrome
• Down's Syndrome features

  • Short
  • Sterile
  • Mental retardation
  • Flat face with a short nose
• How does the incidence of Down's syndrome change with maternal age

  Increases
• Features of Turner's Syndrome

  
  

  
  

  • Sterile due to lack of maturation of sex organs
  • Normal intelligence
• What are the features of Klinefelter's Syndrome

  
  

  • Male with some female characteristics
  • Sterile
  • Sub-normal intelligence
  • Tall stature
• Changes in chromosome structure

  • Deletions
  • Translocations
  • Duplications
  • Inversion
• What causes Prader-Willi Syndrome

  • Deletion in long arm of chromosome 15
  • Only occurs when the affected chromosome is inherited from the father – due to genomic imprinting
• What causes Angelman's Syndrome

  • Deletion in long arm of chromosome 15
  • Only occurs when the affected chromosome is inherited from the mother – due to genomic imprinting
• Genomic imprinting

  The process that affects certain genes, whereby either the maternal or the paternal copy of the gene is silenced
• What is a metacentric centromere

  When the centromere is placed in the center.
• what is a sub-metacentric centromere

  when the centromere is placed off-centre
• What is an acrocentric chromosome

  When the centromere is placed near the end.
• Which arm is the p-arm on a chromosome

  Short
• Which are is the q-arm on a chromosome

  Long
• What are the gametes if non-disjunction takes place in Meiosis 1

  50% trisomy and 50% monosomy
• What are the gametes if monosomy takes place in Meiosis 2

  50% normal. 25% monosomy. 25% trisomy.
• What causes down syndrome

  Trisomy 21
• What conditions are caused by chromosomal deletions

  Cri-du-chat syndrome, prader-willi and angelman syndrome.
• What conditions are caused by chromosomal translocations

  Familial Down's and chronic myelitic leakaemia.
• What causes cri-du-chat syndrome

  Deletion of part of chromosome 5.
• What conditions does genomic imprinting cause

  Angelman and prader-willi syndromes.
• What happens to the chromosomes in familial down's syndrome

  One chromosome 21 is attached to chromosome 14
• What is the karyotype for familial down's syndrome

  t(14;21)
• What is the karyotype for chronic myelitic leukaemia

  t(22;9)
• What is a reciprocal translocation

  When two chromosomes swap genetic information
• What does a reciprocal translocation cause


  Chronic myelitic leukaemia
• What is the pathology of chronic myelitic leukaemia 


  Production of an oncogene results in increased production of leukocytes.