Cyto - Midterms

• Chromosomes


  Coiled DNA

  
• Chromosomes


  • Can be a single (unduplicated) component and replicated
  • Single chromosomes have 46 chromosomes and 46 chromatids
  • Replicated chromosomes have 46 chromosomes and 92 chromatids

  
• DNA can actually reach the sun and back over 600 times. They are very complex and wide.
• Histones


  Proteins that provide the structural support for chromosomes

  
• Homologous chromosome


  Single chromosome
• Most of our somatic cells are single chromosomes which contains 46 chromatids and 23 pairs of chromosomes.

  
• Basis of classification of chromosome shape

  • Unduplicated or homologous chromosome
  • Duplicated chromosome

  
• Chromosome structure


  • P arm - smaller
  • Q arm - longer

  
• Types of chromosomes based on centromere position

  • Metacentric
  • Submetacentric
  • Acrocentric
  • Telocentric

  
• Metacentric chromosome


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


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

  
• Acrocentric chromosome


  Chromosome is near end, long arm, has Knob or satellite, centromere is for the secondary constriction, site for nucleolar organizer region that contains multiple copies of ribosomal genes that is required for RNA synthesis, Satellite DNA = repetitive DNA

  
• Telocentric chromosome


  Near the end of chromosome, not normally found in humans, except those who have genetic syndrome like down syndrome, found in mouse

  
• Chromosome banding


  Staining technique for chromosomes which identifies the normal and abnormal chromosome, stains the mitotic chromosome during metaphase, pattern: stained in bands (light and dark)

  
• Cytogenetic analysis


  1. Cells are grown in culture (blood/WBC, buccal swab, bone marrow, tumor cells, pleural fluids, or amniotic fluids)

  2. Enters metaphase

  3. Mitotic inhibitor (colchicine, vinblastine, paclitaxel, docetaxel, etc.) - prevents mitosis

  4. Arrested in metaphase

  5. Stained and good for chromosome banding
• G banding


  Most common for karyotyping due to its effectiveness, distinct banding patterns, high resolution, good for clinical laboratory
• Karyotype


  The product of Chromosome Banding, an individual's complete set of chromosomes that are based on their size, shape, and number

  
• Autosome


  Chromosomes that are responsible for our individual characteristics, the somatic chromosomes (1-22)

  
• Allosome


  The 23rd chromosome, determines our sexual orientation and characteristics
• Chromosome nomenclature


  Long statement - Chromosome 5, p arm, region 1, band 1, sub band 2 = 5p11.2

  Long statement - Chromosome 21, q arm, region 2, band 1, sub band 4 = 21q21.4

  
• Types of chromosomal abnormalities

  • Structural Abnormalities
  • Numerical Abnormalities

  
• Types of structural abnormalities

  • Duplication
  • Deletions
  • Inversions
  • Translocations
• Duplication


  Doubling of alleles, not in the chromosome, mutation in a part of chromosome doubles

  
• Types of duplication


  • Tandem duplication
  • Displaced duplication
  • Reverse duplication
• Deletions


  Loss of chromosome segment, shortened structure of chromosome, effects depend on the location of which genes are located in the deleted region, if the deletion includes the centromere, it will not undergo meiosis/mitosis, deletions are lethal (ex. Hemophilia)

  
• Heterozygous deletion effects


  • Imbalances in gene products and extra gene copies
  • Normally recessive mutations on the homologous chromo lacking the deletion may be expressed - Pseudodominance
  • Some genes must be presence in two copies to function normally - Haploinsufficient gene

  
• Chromosome deletion in human

  • Cri-du-chat syndrome
  • Worl-Hirschhorn syndrome
  • Williams-Beuren syndrome
  • Prader-Willi syndrome

  
• Inversions


  Segments are turned into 180 degrees, not as lethal
• Types of inversions


  • Paracentric inversions
  • Pericentric inversions
• Translocations


  Entails the movement of genetic materials between non homologous chromosomes or not within the same chromosome, should not be confused with crossing over, there is no exchange

  
• Types of translocations


  • Nonreciprocal translocation
  • Reciprocal translocation
• Numerical chromosomal abnormalities


  • Aneuploidy
  • Polyploidy

  
• Aneuploidy


  Chromosome mutation that includes the changes in the number of chromosomes, only occurs in one set, may arise through nondisjunction - failure of homologous chromosomes to separate during mitosis/meiosis (anaphase), either results in a gain or loss of chromosome/gametes

  
• Polyploidy


  Changes in the number of chromosome sets

  
• Types of aneuploidy

  • Nullisomy
  • Monosomy
  • Trisomy
  • Tetrasomy
• Nullisomy


  Loss of both members of a homologous pair
• Monosomy


  Loss of a single chromosome, 45 total chromosomes

  
• Trisomy


  Gain of a single chromosome in a pair, 47 total chromosomes

  
• Tetrasomy


  Gain of two homologous chromosome, 48 total chromosomes
• Non-disjunction


  Most common reason for aneuploidy of chromosomes during mitosis or meiosis