Chromosomal Abnormalities

• Karotype: A display of the chromosome pairs of a cell

  Metaphse chromosomes are squashed

  Stained with DNA-binding dyes

  Banding patterns help indentify chromosomes
• Metacentric


  Arms of equal length
• Submetacentric


  Long arm and short arm
• Acrocentric


  Long arm and knob
• Telocentric


  Centromere at or very near one end
• Preimplantation Genetic Diagnosis

  Genetic testing on embryos for genes that cause untreatable or severe diseases
• Aneuploidy

  Individual chromosomes added or deleted
• Polyploidy

  Complete sets of chromosomes are added
• Duplication


  Part of the chromosome is repeated
• Segmental Duplication

  Duplications longer than 1000bp
• Deletion


  Part of a chromosome is lost
• Duplications and deletions result from uneven crossing over
• Copy number variations

  Smaller duplications and deletions (found using microarray technology)

  Very common (abt. 1000 per person)

  Many have no phenotypic effect
• Paracentric inversions

  Do not include the centromere
• Pericentric Inversions

  Involve the centromere
• Translocation


  Movement of genetic material betwenn non-homologous chromosomes
• Robertsonian Translocation


  Long arms of two non-homologous chromosomes fuse at the centromere forming a single chromosome. They are reciprocal translocations that involve acrocentric chromosomes (these chromosomes are entirely at one end).
• Aneuploidy Causes

  Loss of centromere, robertsonian translocation, nondisjunction
• Nondisjunction

  Failure of homologous chromosomes to separate properly during meiosis or mitosis
• Types of Aneuploidy

  Nullisomy, monosomy, trisomy, tetrasomy
• Affects of Aneuploidy

  Only 9 types recognized in newborns. Affect 5%+ of pregnancies but only 0.1% of live births
• Trisomy 21

  Down syndrome ( 3 copies of chromosome 21)

  Maternal Age is a risk factor
• Trisomy 18

  Edward's syndrome

  Second-most common autosomal trisomy (1 in 8000 live births)

  Seen with clenched fists
• Trisomy 13


  Patau syndrome1 in 15,000 live births

  Serious medical and physical abnormalities
• Mosaicism


  A condition in which cells within the same person have a different genetic makeup. (ex: turner syndrome,55% are mosaics)

  Nondisjuction during mitosis in early development

  -Patches of cells are normal and other patches have abnormality
• Mosaic Trisomy 8


  Very rare in live birthds (1 in 25,000-50,00)

  Complete trisomy 8 is not compatible in live

  Mosaicism results from nondisjunction

  Intellectual disability, facial abnormalities, normal lifespan
• Uniparental Disomy


  Both copies of a chromosome are inherited from one parent

  Results in unexpected inheritance patterns
• Polyploidy

  Not viable in humans

  Only one viable animal (Argentina Rat)

  Found in some invertbrates, fish, salamanders, frogs, and lizards

  Common in plants

  
  

  Used in agriculute to produce larger leaves or fruits
• Autopolyploidy


  Three or more homologous chromosome per cellAll chromosomes from a single species

  Meiosis results in unbalanced gametes (not viable)

  
  

  Used in agriculutre to produce seeds watermelons
• Allopolyploidy

  Hybridization of gametes from two species2n but not homologous, but they are not homologousWill not pair and separate properly (no viable gametes)