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FISH in PGD and PGS

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 biopsyblastomere biopsy and trophoblast biopsy), the DNA probe is added and the cell is visualized under a microscope.

Gallery of FISH images

PGD: Blastomere biopsy: Trisomy 21

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Blastomere biopsy: Trisomy 21
The cell pictured here is one cell (blastomere) taken from an eight cell embryo. Fluorescent in situ hybridization was performed for two chromosomes (Two color FISH): Chromosomes number 18 and 21. […]

PGD: Blastomere biopsy: Triploid embryo

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PGD: Blastomere biopsy: Triploid embryo
The cell pictured here is one cell Fluorescent in situ hybridization was performed for two chromosomes (Two color FISH): Chromosomes number 18 and 21. Both chromosomes tested have an extra (third) copy. […]

PGD: Polar body biopsy: Trisomy 21

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PGD: Polar body biopsy: Trisomy 21
This image shows the 1st polar body. Two chromosomes are being tested here which are shown in green and orange. In a normal embryo, there should be two green dots and two orange dots. […]

PGD: Polar body biopsy monosomy 21

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PGD: Polar body biopsy monosomy 21
This image shows the 1st polar body. Two chromosomes are being tested here which are shown in green and orange. In a normal embryo, there should be two green dots and two orange dots. […]

PGD: Blastomere biopsy with three color FISH

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PGD: Blastomere biopsy with three color FISH
In this example, a patient has undergone IVF with PGD to determine if there are abnormalities in the number of chromosomes. The cell pictured here is one cell (blastomere) taken from an eight cell embryo. […]

PGD: Polar body biopsy with three color FISH

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PGD: Polar body biopsy with three color FISH
In this example, a patient has undergone IVF with PGD to determine if there are abnormalities in the number of chromosomes. The 1st polar body pictured (PB1) is normal for the two chromosomes being tested. […]

PGD: Polar body biopsy with two color FISH

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PGD: Polar body biopsy with two color FISH
In this example, a patient has undergone IVF with PGD to determine if there are abnormalities in the number of chromosomes. The 1st polar body pictured (PB1) is normal for the two chromosomes being tested. […]