Fluorescence In Situ Hybridization (FISH)

Definition - What does Fluorescence In Situ Hybridization (FISH) mean?

Fluorescence in situ hybridization (FISH) is a technique used to spot chromosomal abnormalities that are barely discernible by standard chromosomal testing. Using the FISH technique, it is possible to visualize the genetic material in a person's or embryo's cells, including specific genes or sections of genes. This analysis looks for abnormal changes in the number and structure of the chromosomes, such as deletions (or losses or monosomy) and duplications (gains) of genetic material, which might signal birth defects or developmental delays.

FertilitySmarts explains Fluorescence In Situ Hybridization (FISH)

The FISH technique has a number of applications:

  • It can examine the number of chromosomes in cases of recurrent in-vitro fertilization failure or recurrent pregnancy loss (RPL) and therefore serves as a diagnostic tool for couples undergoing infertility treatment. For recurrent IVF failure, the technique has a major role in preimplantation genetic diagnosis (PGD) in detecting embryos with an abnormal number of chromosomes (aneuploidy).
  • It can also help evaluate the chromosome abnormalities in men with a reduced sperm count (oligozoospermia).
  • The FISH technique can also detect genetic abnormalities like Down syndrome.
  • It can also help distinguish between different types of partial moles in women with molar pregnancies.

The technique uses probes that are single DNA strands labeled with a fluorescent dye. When applied to a cell, these probes bind to the complementary (or matching) strand of DNA to allow the formation of complexes or hybrids. When the probes attach to a chromosome, the fluorescent tag facilitates the identification of their location.

The hybridization period continues for about 24-hours, after which the specimen is ready to be viewed under a fluorescent microscope. If the number of chromosomes is normal, two of the marker probes will hybridize and are visible under the microscope. However, if there is an abnormality, such as a small deletion in the zone complementary to the probe, the probe will fail to hybridize; whereas, with an extra chromosome (trisomy), an extra probe would be visible.

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