Karyotyping

• What is a karyotype?


  The number and appearance of chromosomes in the nucleus of a eukaryotic cell
• What does karyotyping analyze?


  Presence or absence of individual chromosomes, chromosomal aberrations, and sex chromosome content
• What physical characteristics are examined in a karyotype?


  Length, position of the centromere, banding pattern, and differences between sex chromosomes
• What is the purpose of genetic counseling?


  To determine the genetic odds that offspring may carry a particular negative or lethal trait
• What is the procedure called to check for chromosomal abnormalities?

  Karyotyping
• What samples can be used for karyotyping?


  Blood, bone marrow, skin, amniotic fluid, and extraembryonic cells
• What role do lectins play in karyotyping?


  They stimulate mitosis
• What is the function of colchicine in karyotyping?


  It arrests mitosis at metaphase
• Why is a hypotonic solution used in karyotyping?


  It provides more room for chromosomes to spread out as the cell enlarges
• What is karyology?


  The study of whole sets of chromosomes
• What is a karyogram or idiogram?


  A way to depict chromosomes organized into homologous pairs arranged by size
• What are the variations in chromosome morphology?

  • Deletion: part of chromosome is deleted
  • Duplication: segment breaks off and attaches to homologous chromosome
  • Inversion: segment is excised and reintegrated at 180° orientation
  • Translocation: segment breaks off and attaches to non-homologous chromosome
  • Euploidy: complete set of chromosomes is present
  • Aneuploidy: gaining or losing one chromosome
  • Monosomy: loss of single chromosome
  • Trisomy: gain of single chromosome
  • Polyploidy: more than two sets of chromosomes are present
  • Triploid: 3 sets (69 chromosomes)
  • Tetraploid: 4 sets (92 chromosomes)
• What is nondisjunction?


  The failure of homologs or sister chromatids to separate in meiosis or mitosis
• How is staining used in the study of karyotypes?


  It allows visualization of chromosomes after cells are arrested during division
• What type of cells are most frequently used for karyotyping in humans?


  White blood cells
• What is a Barr body?


  The inactive X chromosome in a female somatic cell
• What is Lyonization?


  The inactivation of an X chromosome transforming it into a Barr body
• What cells can be used for chromosomal analysis?


  • Any cell with a nucleus
  • Lymphocytes
  • Skin cells
  • Tumor cells
  • Amniotic cells
  • Chorionic villi
  • Rare fetal cells from maternal blood
• What is the first step in the karyotyping procedure?


  5 mL of blood is removed from the patient
• How is amniotic fluid collected for karyotyping?


  Using a large syringe guided by ultrasound
• What happens to the cells after they are cultured in karyotyping?


  Mitosis is stopped at metaphase using chemicals
• How are chromosomes arranged in a karyotype?


  They are cut out and arranged in pairs according to size and location of the centromere
• How are chromosomes grouped in a karyotype?


  • Group A: 1-3, largest, median
  • Group B: 4-5, large, submedian
  • Group C: 6-12, medium, submedian
  • Group D: 13-15, medium, acrocentric
  • Group E: 16-18, short, median or submedian
  • Group F: 19-20, short, median
  • Group G: 21-22, very short, acrocentric
  • Chromosome X: similar to group C
  • Chromosome Y: similar to group G
• What is spectral karyotyping?


  A technique to visualize all pairs of chromosomes in different colors
• What is the purpose of FISH in cytogenetics?


  To label a known chromosome sequence with DNA probes for visualization
• What is the Philadelphia chromosome associated with?


  Chronic myeloid leukemia (CML)
• What is the significance of the translocation in the Philadelphia chromosome?


  It involves a translocation between chromosomes 9 and 22
• What does the abl gene encode?


  A tyrosine kinase
• What is the bcr gene associated with?


  It is part of the breakpoint cluster region in the Philadelphia chromosome
• What are the different banding techniques used in cytogenetics?

  • G-banding: Giemsa stain after trypsin digestion
  • R-banding: Reverse of G-banding
  • C-banding: Stains centromeres
  • Q-banding: Fluorescent pattern using quinacrine
  • T-banding: Visualizes telomeres
• What is G-banding used for?


  To produce a series of lightly and darkly stained bands on chromosomes
• What does R-banding reveal?


  It produces bands complementary to G-bands
• What is the purpose of C-banding?


  To stain constitutive heterochromatin at the centromeres
• What does Q-banding visualize?


  A fluorescent pattern obtained using quinacrine for staining
• What does T-banding visualize?


  Telomeres using silver staining
• What is digital karyotyping?

  A technique used to quantify the DNA copy number on a genomic scale
• What is the fundamental number (FN) of a karyotype?


  The number of visible major chromosomal arms per set of chromosomes
• How does the FN relate to humans?


  Humans have FN = 82 due to five acrocentric chromosome pairs
• What is the role of FISH probes?


  To detect chromosome number abnormalities and specific gene locations
• What are the types of FISH probes?


  • Chromosome specific probes: for detection of chromosome number abnormalities
  • Painting probes: highlight whole chromosomes for detecting translocations