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Chromosomal abnormalities

Normal chromosomal arrangement

  • Normal cells: 44 autosomes + 2 sex chromosomes
  • 0,23,46, 46(n) - normal number of chromosomes in a cell (eg. RBC has none, striated muscle 46n)
0 23 46
46n
Erythrocytes Haploid cells
Gonads - sperm, oocytes		 Normal cells Tetraploid - before division
Multinucleated cells - osteoclasts, syncitiotrophoblasts, muscle cells

Classification Chromosome abnormalities

 

  Autosome Sex chromosome
Structure
  • Translocations - one part onto another
  • Delections - loss of material
Number
  • Monosomy - loss of one pair of chromosomes
    1. Turners XO
  • Trisomy - increase to three of one type of chromosom
    1. Downs Chromosome 23
    2. Edwards
    3. Patau
  • Polyploidy - extra sets of entire chromosomes
    1. Kleinfelter's
Location
  

 

 

Autosomal dominant
 Autosomal recessive  X-linked 
  • Single copy of gene responsible for disease
  • Both copies of abnormal gene must be present
  • Disease due to abnormality on X-chromosome
  • FAP
  • APKD
  • Achondroplasia
  • Marfan's (fibrillin)
  • Spherocytosis (spectrin)
  • Cystic fibrosis (7q CFTR)
  • Alpha-1-Anti-trypsin deficiency
  • Haemophilia A/B
  • G6PD
  • Fragile X
  • Red-green colour blindness
  • Red-green colour blindess (1/10)

 

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