Karyotyping

Overview – Karyotyping

• Function
  • examine chromosomal structure
• Process 
  • mitotic cells in metaphase selected from actively dividing cell population
    • white cells, bone marrow, placenta, amnion
    • when chromosomes are most condensed
  • chromosomes are stained with or without G-banding
    • G-banding involves partial digestion with trypsin
      • leaves alternating dark and white bands
    • staining with Giemsa or other stains which have affinity for DNA
  • spectral karyotyping
    • 5 different fluorescent probes are added
    • special digital image processing colors each chromosomes differently
  • chromosomes are ordered, numbered based on unique properties of all 23 chromosomes
• Clinical use
  • can analyze whether a gross chromosomal abnormality exists
    • ex.) trisomy, monosomy 
  • used commonly for prenatal diagnosis via chorionic or amniotic sampling
• spectral karyotyping can also diagnose translocations, inversions, or deletions of specific chromosomal segments if the change is large

Introduction

Karyotyping is a laboratory technique used to examine the chromosomes of an individual. Chromosomes are the structures in cells that carry genetic information, and karyotyping involves the visualization and analysis of these chromosomes to identify abnormalities or genetic disorders. It can be performed on cells from any tissue, including blood, amniotic fluid, and placental tissue.

During karyotyping, cells are grown in a laboratory and then arrested in the metaphase stage of cell division. At this stage, the chromosomes are condensed and can be stained to reveal their characteristic banding patterns. The stained chromosomes are then examined under a microscope, and a picture of the chromosome set, or karyotype, is created.

How the Test Is Performed

Karyotyping is typically performed on cells that are actively dividing, such as white blood cells in the blood or cells from amniotic fluid during pregnancy. The procedure for collecting the cells varies depending on the type of sample being collected.

For a blood sample, a healthcare provider will first clean the area around the puncture site with an antiseptic solution. They will then insert a needle into a vein and collect a small sample of blood. The blood sample is then sent to a laboratory, where the white blood cells are separated from the other components of the blood and grown in culture.

For prenatal testing, a sample of amniotic fluid is collected through a needle inserted through the mother’s abdomen and into the uterus. The amniotic fluid contains fetal cells, which can be used for karyotyping.

Once the cells have been collected and cultured, they are treated with a chemical to arrest them in the metaphase stage of cell division. This allows the chromosomes to be stained and visualized under a microscope. The chromosomes are then arranged in pairs according to their size, shape, and banding patterns, and a karyotype is created.

The karyotype is then analyzed to identify any abnormalities, such as extra or missing chromosomes, translocations, or deletions. The results of the analysis are typically reported as a written description of the chromosome abnormalities or as a visual representation of the karyotype.

Types

1. Standard karyotyping: Standard karyotyping involves the analysis of the chromosomes to determine their number and any structural abnormalities. This is the most common type of karyotyping and is used for a range of diagnostic purposes, including prenatal testing, cancer diagnosis, and evaluation of infertility.
2. Fluorescence in situ hybridization (FISH): FISH is a type of karyotyping that uses fluorescent probes to detect specific genes or chromosomal regions. This technique is often used to identify chromosomal abnormalities that are too small to be seen by standard karyotyping.
3. Comparative genomic hybridization (CGH): CGH is a type of karyotyping that compares the DNA content of a patient’s cells to a reference sample. This can be used to identify chromosomal abnormalities that are too small to be seen by standard FISH.
4. Array-based comparative genomic hybridization (aCGH): aCGH is a type of karyotyping that uses microarrays to compare the DNA content of a patient’s cells to a reference sample. This technique can identify chromosomal abnormalities with high resolution and is often used for research or diagnostic purposes.

Studies

1. Prenatal diagnosis: Karyotyping is commonly used during prenatal testing to detect chromosomal abnormalities in fetuses. This can be done through chorionic villus sampling (CVS) or amniocentesis. These tests are usually recommended for pregnant women who are at increased risk of having a baby with a genetic disorder or abnormality.
2. Cancer diagnosis and treatment: Karyotyping can be used to diagnose various types of cancer, as many types of cancer cells have abnormal chromosomes. Karyotyping can also be used to monitor the progress of cancer treatment and to detect any genetic changes that may occur in cancer cells over time.
3. Identification of genetic disorders: Karyotyping can be used to diagnose a wide range of genetic disorders, such as Down syndrome, Turner syndrome, and Klinefelter syndrome, which are caused by chromosomal abnormalities. Karyotyping can also be used to identify other genetic disorders that are associated with specific chromosomal changes.
4. Research: Karyotyping is commonly used in research to study the structure and function of chromosomes. It can be used to identify new genetic mutations, study the genetics of diseases, and explore the role of chromosomes in inheritance.

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