Biology · MU Sofia

40. Methods of karyotyping and chromosome analysis.

Covers how karyotyping samples are collected, cultured, arrested at metaphase, swollen, fixed and slid, then the classical banding methods (G, R, C, T, NOR and Q) and what each reveals. Explains idiograms and molecular cytogenetics via FISH, including probe types and examples such as BCR-ABL. Includes a mnemonic for the preparation steps, one for the banding methods, a FISH probe table and a classical-versus-molecular comparison table.

Inside: 9 sections · 2 labelled pictures · 3 tables · 14 flashcards · 7 min

Topic 41 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 9 sections, about 950 words (7 min of reading), with 14 flashcards.

In this note

  1. Methods of karyotyping and chromosome analysis.
  2. Understanding Cytogenetics
  3. Sample Collection and Preparation for Karyotyping
  4. Classical Chromosome Banding Techniques
  5. Idiograms
  6. Molecular Cytogenetics: Fluorescent In Situ Hybridization (FISH)
  7. MNEMONICS
  8. 🔬 3. FISH Probe Types & Uses
  9. 🧠 4. Classical vs Molecular Cytogenetics

Understanding Cytogenetics

  • Cytogenetics is the branch of genetics that focuses on the study of chromosomes, their structure, function, and behavior during cell division
  • It helps identify numerical and structural abnormalities in chromosomes that cause genetic disorders
  • This field uses both classical techniques like banding and advanced molecular techniques to analyze chromosomal changes
  • Applications include diagnosing genetic diseases, detecting cancer-associated chromosomal changes, and guiding reproductive counseling

Sample Collection and Preparation for Karyotyping

  • Cells used for karyotyping must be capable of undergoing active division, especially reaching the metaphase stage where chromosomes are most visible
  • Common sample sources include peripheral blood lymphocytes, bone marrow, chorionic villi, amniotic fluid cells, and solid tissues
  • Collected cells are cultured in nutrient media to encourage mitotic division
  • A mitotic inhibitor such as colchicine is added to arrest cells at metaphase by disrupting spindle fiber formation
  • The cells are treated with a hypotonic solution to swell them, making chromosomes spread out more clearly
  • Cells are then fixed using a mixture of methanol and acetic acid which preserves DNA and removes proteins and water
  • Fixed cells are dropped onto microscope slides for staining and visualization

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