CYTOGEN MIDTERMS

• Chromosomes


  • Coiled
  • Involved with the packing of DNA
  • Proteins that provide structural support are Histones

  
• DNA Chromosomes


  Can be a single (unduplicated) component and replicated

  
• Homologous chromosome


  One chromosome (unduplicated)

  
• Chromosome replication

  1. Single chromosomes have 46 chromosomes and 46 chromatids (during interphase S phase)

  2. Replicated chromosomes have 46 chromosomes and 92 chromatids (after metaphase or during anaphase)

  
• Our DNA can actually reach the sun and back over 600 times
• Naturally, most of our somatic cells are single chromosomes which contains 46 chromatid, 46 chromosomes and 23 pairs of chromosomes called homologous chromosomes

  
• Types of chromosomes based on centromere position

  • Metacentric
  • Submetacentric
  • Acrocentric
  • Telocentric

  
• Metacentric


  • Located in the middle, almost equal length, p arm is a bit shorter than q arm
• Submetacentric


  • Displaced on one end, short arm (p region), long arm (q region)
• Acrocentric


  • Near end, long arm, knob or satellite
• Telocentric chromosomes are not normally found in humans

  
• Chromosome banding


  Staining technique to identify normal and abnormal chromosomes

  
• Chromosomes are stained during metaphase because this is where the replicated chromosomes align in the middle and are more condensed

  
• Cytogenetic analysis


  1. Cells are grown in culture

  2. Enters metaphase

  3. Mitotic inhibitor is used to arrest in metaphase

  4. Stained and good for chromosome banding
• Karyotype


  An individual's complete set of chromosomes based on their size, shape and number

  
• Chromosome types

  • Autosome (1-22)
  • Allosome (23)

  
• Chromosomal abnormalities


  Changes in the structure or number of chromosomes
• Types of chromosomal abnormalities

  • Structural abnormalities
  • Numerical abnormalities
• Structural abnormalities


  • Duplications
  • Deletions
  • Inversions
  • Translocations
• Duplications


  • Duplicate or replicate (copy) the structural is more on the allele
  • Mutation in which of the chromosomes has been doubled
• Deletions


  • Loss of chromosome segment (naging shortened yung structure ng chromosome)
  • It will not segregate in meiosis or mitosis and usually be lost
  • Become lethal
• Effects of deletions
• Inversions


  • Paracentric inversions (does not include the centromere)
  • Pericentric inversions (includes the centromere)
• Translocations


  • Nonreciprocal translocation (genetic material moves from one chromosome to another)
  • Reciprocal translocation (exchange of segments)
• Numerical abnormalities


  • Loss or gain of a whole chromosome
  • Include autosome (somatic cells) and sex chromosomes
  • Chromosome loss has a greater effect than chromosome gain
• Aneuploidy


  Chromosome mutation that includes changes in the number of chromosomes
• Polyploidy


  Change in the number of chromosome sets
• Types of aneuploidy


  • Nullisomy (loss of both members of a homologous pair)
  • Monosomy (loss of single chromosome)
  • Trisomy (gain of single chromosome)
  • Tetrasomy (gain of 2 homologous chromosomes)
• Chromosomes 1-22 are somatic cells, XY are sex cells
• Not all Down Syndrome cases are genetic, some are due to mitotic error
• Nondisjunction


  The most common reason for aneuploidy, occurs in mitosis or meiosis
• Common chromosomal disorders in aneuploidy

  • Trisomy 21 (Down Syndrome)
  • Trisomy 18 (Edwards Syndrome)
  • Trisomy 13 (Patau Syndrome)
  • Monosomy X (Turner's Syndrome)
• Trisomy 21 (Down Syndrome)


  • Most common trisomy, 92% have triple copies
  • Primary Down Syndrome arises from spontaneous egg formation in meiosis 1 (maternal)
  • Familial Down Syndrome caused by translocation between chromosomes 21 and 14
• Characteristics of Down Syndrome

  • Growth delays
  • Immune system problems
  • Flattened facial features
  • Epicanthal folds of the eyes
  • "Simian crease" on the palm
• Trisomy 18 (Edwards Syndrome)


  • Second most common syndrome, 80% of infants die within a year, 13% live to 10 years
• Characteristics of Edwards Syndrome

  • Heart defects
  • Kidney defects
  • Omphalocele
  • Micrognathia
  • Microcephalic skulls
  • 2nd and 5th fingers overlapping 3rd and 4th
• Trisomy 13 (Patau Syndrome)


  • 95% die in the first 3 months of life
• Characteristics of Patau Syndrome

  • Heart defects
  • Kidney defects
  • Cleft palate
  • Holoprosencephaly
  • Polydactyl
  • Muscle weakness
  • Intellectual disability
• Monosomy X (Turner's Syndrome)


  • Single X chromosome
• Characteristics of Turner's Syndrome


  • Swollen hands and feet (in infants)
  • Short stature
  • Webbed neck
  • A high palate
  • Low set ears
  • Obesity
  • Droopy eyelids
  • Flat feet