Structure of chromosomes

The genetic materials that make up the DNA in chromosomes are called nucleotides. There are four nucleotides which are known by there 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 PGD in IVF uses FISH

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 (see polar body biopsy and blastomere biopsy), the DNA probe is added and the cell is visualized under a microscope.

PGD: Polar body biopsy with two color FISH

FISH with analysis for two chromosomes.

PGD: Polar body biopsy for three chromosomes

FISH analysis for three chromosomes

PGD: Blastomere biopsy with three color FISH

PGD of the blastomere pictured is normal for the three chromosomes tested

PGD: Examples of abnormal embryos

Last Updated ( Monday, 17 March 2008 )