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Cytogenetics (Karyotype (Creating karyotype (take 4-6ml of blood, add to…

- - - - Lymphocytes
      - Skin cells
      - Tumour cells
      - Amniotic Cells
      - Chorionic Villi
      - Rare Foetal cells from maternal cells
  - - - G-Banding
      - R-Banding
      - C-Banding
    - - Most commonly used
      - trypsin added to digest part of chromosome
      - Binds with phosphate groups of DNA
      - Types of bands
        
        Dark bands
        
        tightly wound DNA
        
        Light bands
        
        Loosely wound DNA
    - - Fluorescent dyes specific for each chromosome
      - Easily identify chromosomal abnormalities
      - Human cancer cells have a different spectral karyotype
      - Easily identify large scale changes
  - - - Number of chromosomes
      - Sex chromosome content
      - Presence/absence of chromosome
      - Nature or extent of chromosomal aberrations
      - Practices
        
        Amniocentesis
        
        Done in high risk pregnancy
        
        Fluid collected from around foetus
        
        Used for karyotype analysis
        
        Chorionic Villus Sampling
        
        Risk to mother and foetus
        
        Done earlier (8-10) weeks
- - - - in 10000 embryos, 800 will have abnormality's
      - Types
        
        Aneuploidy
        
        Sex chromosome
        
        Examples
        
        XYY syndrome
        
        47,XYY
        
        2 more items...
        
        Klinefelter syndrome
        
        47,XXY
        
        5 more items...
        
        The balance of sex chromosomes is essential for normal development
        
        Addition of chromosomes interferes with normal development
        
        Loss or gain of a sex chromosome
        
        Much more common (1/400 or 1/650)
        
        differing from normal number of chromosomes, but not by a complete set
        
        Polyploidy
        
        Example
        
        Aneuploidy
        
        Can occur at two points in meiosis
        
        Trisomy
        
        7 more items...
        
        Monosomy
        
        3 more items...
        
        Thought to occur as a result of non-disjunction
        
        Addition/deletion of individual chromosomes
        
        Tetraploidy
        
        thought to arise when cell division fails to complete
        
        Mosaic individuals
        
        Uncommon
        
        Lethal
        
        4 copies of each chromosome
        
        Triploidy
        
        three different types
        
        69,XYY
        
        69,XXX
        
        69,XXY
        
        rarely survive more than 1 month
        
        99% result in miscarriage
        
        Most common (1% of conceptions)
        
        3 copies of each chromosome
        
        Three major causes
        
        Errors in mitosis after fertilisation
        
        Events at fertilisation
        
        Errors in meiosis and gamete formation
        
        extra set of chromosomes
      - 750 miscarry, 50 survive
    - - Types
        
        Duplication
        
        Copying of a portion of the chromosome
        
        Generates extra genetic material
        
        Benefits
        
        Adaptive immune system
        
        Harms
        
        PMP22 duplication results in Charcot-Marie-Tooth disease
        
        progressively curled toes, feet and arched heels
        
        reduced sensitivity to heat and cold
        
        Deletion
        
        A potion of chromosome is lost
        
        can be small or large
        
        Harmful
        
        Loss of 7q11.23
        
        Williams syndrome
        
        elf appearance
        
        6 more items...
        
        Inversion
        
        portion of chromosome flipped
        
        two chromosomal breaks
        
        Types
        
        Paracentric
        
        flip happens on end
        
        Pericentric
        
        Flips on centromere
        
        Effects
        
        Genetic material may be lost
        
        Genes disrupted
        
        Large Inversions may make it difficult for chromosomal pairing
        
        Reciprocal translocation
        
        Genetic material is swapped between two non homologues chromosomes
        
        effects
        
        generally not loss or gain of material
        
        Gene disruption
        
        Chronic Myeloid leukaemia
        
        9q and 22q
        
        balanced or unbalanced gametes
        
        results in miscarriage or other abnormality
        
        Quadriradial chromosome pairing
        
        four chromosomes pairing
        
        Robertsonian translocation
        
        Centromeres of acrocentric chromosomes fuse
        
        short arm normally lost
        
        Effects
        
        Unbalanced gamete formation can have downstream effects
        
        Robertsonian translocation
    - - Uniparental disomy
        
        Both copies of a chromosome inherited from one parent
      - Copy number variations
        
        small scale duplications or deletions
      - Fragile sites
  - - - provide addresses
      - divide arms into regions and bands
    - - Acrocentric
        
        Short arms composed of satellite and stalk and long arms normal
      - Sub metacentric
        
        Shorter short arm and longer long arm
      - Metacentric
        
        Same sized short and long arm
  - - - contain only one copy of each chromosome
        
        23 in total
  - - - Chromosomes 1-22
      - Chromosomes other than sex chromosomes
        
        X and Y variations
        
        involved in sex determination