CYTOGENETICS

• 1. banded chromosome analysis


  Technique to analyse chromosomes by staining them with Giemsa dye to produce a banding pattern
• Mutation described


  Translocation between chromosomes 9 and 22, t(9;22)(q34;q11.2)
• Translocation


  • Structural abnormality involving rearrangement of chromosomal material
• FISH


  Fluorescence in situ hybridization, a technique that complements standard chromosome analysis
• Human cytogenetics is the study of chromosomes, their structure, and their inheritance
• There are approximately 23,000 genes in the human genome, most of which reside on the 46 chromosomes normally found in each somatic cell
• Chromosome disorders


  • Structural
  • Numeric
• Chromosomal abnormalities are observed in approximately 0.65% of all live births
• The gain or loss of an entire chromosome, other than a sex chromosome, is usually incompatible with life and accounts for approximately 50% of first-trimester spontaneous abortions
• In leukemia, cytogenetic abnormalities are observed in more than 50% of bone marrow specimens
• Reasons for chromosome analysis

  • Intellectual disability
  • Infertility
  • Ambiguous genitalia
  • Short stature
  • Fetal loss
  • Risk of genetic or chromosomal disease
  • Cancer
• Cell cycle


  Divided into 4 stages: G1, S, G2, M
• Chromosome


  Formed from a double-stranded DNA molecule that contains a series of genes
• Metaphase


  Stage of mitosis where chromosomes align on the equatorial plate
• Chromosome structure


  • DNA double helix
  • Nucleosomes
  • 30nm chromatin fiber
  • Loops extending from main chromosome axis
• Chromosome number


  Diploid (46) and haploid (23)
• Chromosome types


  • Metacentric
  • Submetacentric
  • Acrocentric
• Chromosome preparation


  1. Tissue harvesting

  2. Cell culture

  3. Mitotic arrest

  4. Hypotonic treatment

  5. Fixation

  6. Slide preparation
• Chromosome banding


  Staining techniques like Q-banding and G-banding to produce unique banding patterns for each chromosome
• Chromosome


  Derived from the Greek words chroma (color) and soma (body), meaning "colored body"
• Chromosome staining with fluorochrome dye


  • Allows distinguishing a banding pattern unique to each chromosome
  • Differentiates the chromosome into bands of differing widths and relative brightnesses
• Brightly fluorescent bands of human chromosomes

  • Distal end of the Y chromosome
  • Centromeric regions of chromosomes 3 and 4
  • Short arms of the acrocentric chromosomes (13, 14, 15, 21, and 22)
• 1. banding


  Stains AT-rich areas of the chromosome, with dark bands called G-positive(+) and guanine-cytosine-rich areas called G-negative(-)
• 1. banding


  Stains the centromere and surrounding condensed heterochromatin
• Nucleolar organizer regions (NORs)


  Contain tandemly repeated ribosomal nucleic acid (RNA) genes
• By examination of human chromosomes early in mitosis, it has been possible to estimate a total haploid genome (23 chromosomes) with approximately 2000 AT-rich (G+) bands
• The later the stage of mitosis, the more condensed the chromosome and the fewer total G+ bands observed
• Metaphase analysis


  1. Scan for metaphase cell

  2. Analyze chromosome number

  3. Analyze banding pattern

  4. Record summary as karyotype
• Fluorescence in situ hybridization (FISH)


  Molecular technique using DNA/RNA probes labeled with fluorophores to detect chromosomal abnormalities
• Advantages of FISH


  • Can analyze both dividing and non-dividing cells
  • Provides quick test results within 24 hours
  • Can be performed on various sample types
• Cytogenetic nomenclature


  • Uniform code used to communicate chromosome abnormalities
  • Designates chromosome arms, regions, and specific bands
• Numeric abnormalities and structural changes are the two major categories of chromosome abnormalities
• t(12;21)(p13;q22)


  Translocation between the short arm of chromosome 12 at band p13 and the long arm of chromosome 21 at band q22
• Semicolon


  Used to separate the chromosomes and the band designations
• Derivative chromosome


  A translocated chromosome
• der(12) and der(21)


  Chromosomes 12 and 21 after translocation
• Deletion


  Abbreviation del preceding the chromosome
• No spaces are entered in these designations except between abbreviations
• Types of chromosome abnormalities

  • Deletions
  • Inversions
  • Ring formations
  • Trisomies
  • Polyploidy
• Numeric abnormalities


  Defects involving an abnormal number of chromosomes