FISH in PGD and PGT

Structure of chromosomes

The genetic materials that make up the DNA in chromosomes are called nucleotides. There are four nucleotides which are known by their abbreviations A,G,C, and T. You have probably heard that the two strands of DNA are called a double helix. The DNA double helix is held together by attachment of the nucleotides. A always attaches to T and G always attaches to C.

DNA FISH Probes

Using this knowledge, we can make a small segment of DNA (called a DNA probe) that will attach to the DNA of a chromosome. Each chromosome will have some unique areas of DNA that no other chromosome has. A unique DNA probe can be made that recognizes only one specific chromosome.

Making the FISH probe visible

Once a DNA probe has been made, a chemical can be attached that will make it glow using ultraviolet light under a microscope. These chemicals are called flourophores and there are many different colors available. A different color can be used for each chromosome that you want to study so that you can tell the different chromosomes apart. For example, green might represent chromosome 21 and red might be chromosome 18.

FISH – Flouresecent in-situ hybridization

During FISH, a portion of the embryo containing chromosomes is removed. This is called a biopsy. Embryos can be biopsied at different stages during their development. See polar body biopsy, blastomere biopsy and trophoblast biopsy), the DNA probe is added and the cell is visualized under a microscope.