CYTOLOGY

• Chromosome


  Consist primarily of DNA(coiled) and proteins; duplicated and transmitted via cell division
• Chromosome


  • HETEROCHROMATIN (DARK)-contains highly repetitive DNA sequence
  • EUCHROMATIN (LIGHT)- protein-encoding sequences

  
• Homologous chromosomes


  Chromosomes in a homologous pair each have the same genes in the same order, but there may be variation between them, resulting in different alleles
• Essential parts of the chromosome

  • Telomeres
  • Origin of replication sites
  • Centromere
• Telomeres


  • Chromosome tips; each repeats the sequence TTAGGG
  • Shorten with each mitotic division
• Centromere


  • Largest constriction of chromosome; where spindle fibers attach during cell division
  • Replicate toward the end of S phase of the cell cycle
  • Vanishes as soon when cell division began
• Karyotypes


  • Reveals certain conditions that the DNA sequencing miss
  • Displays chromosomes by size and physical land marks

  
• Karyotype grouping


  • Group A: Large metacentric chromosome
  • Group B: Large submetacentric chromosome
  • Group C: Medium-sized submetacentric chromosome
  • Group D: Medium-sized acrocentric chromosome with satellites
  • Group E: Moderately short metacentric or submetacentric chromosome
  • Group F: Short metacentric chromosomes
  • Group G: Short acrocentric chromosome with satellites, Y chromosome does not bear any satellite
• Allosome (sex) chromosomes


  Chromosomes that carry the genes that determine the sex of an individual and secondary sexual characteristics
• Autosome (somatic) chromosomes


  Chromosome pair 1-22; responsible for our individual/ unique characteristic
• Centromere positioning


  • Metacentric
  • Submetacentric
  • Acrocentric
  • Telocentric
• Metacentric chromosome


  • Centromere divides it into two arms of approximately equal length
  • p arm is a bit shorter than the q arm
• Submetacentric chromosome


  • Establishes one long arm and a short arm
  • Centromere is off-center, so that one chromosome arm is longer than the other
• Acrocentric chromosome


  • Pinches off only a small amount of material toward one end
  • Centromere is near on one end, which serves as the primary constriction
  • Producing a Long arm (q arm) and a Knob or Satellite (p arm)
  • Blob-like ends present in five human chromosomes (13, 14, 15, 21, and 22)
  • Satellite DNA are responsible for the uniqueness of humans (TANDEM REPEATS)
• Humans do not contain telocentric chromosomes
• Chromosome banding


  Staining technique for chromosomes to identify the normal and abnormal chromosomes; stained during metaphase

  
• Cytogenetic analysis


  • Cells are grown in culture
  • Enters metaphase
  • Mitotic inhibitor used (Colchine, Vinblastine, Paclitaxel, Docetaxe)
  • Arrested in metaphase
  • Stained and good for chromosome banding
• Chromosome banding techniques


  • G banding
  • R banding
  • Q banding
  • C banding
• Chromosome nomenclature