Types of Genetic Testing

DNA is a type of molecule in all cells of the body. DNA is passed on to each person from their parents (inherited) in bundles of DNA called chromosomes. Usually, each person gets 23 chromosomes from their father and 23 from their mother. The chromosomes contain genes that carry important instructions for how cells grow, function, and die. These genes determine traits such as eye or skin color, and height.

Sometimes, people may get extra chromosomes or pieces of them from their parents. Other times, they may be missing whole chromosomes or pieces. People may also have changed DNA (called variants). These changes may cause the body not to work properly, or they may increase a person’s risk for diseases such as cancer. Variants in genes that can cause disease are also known as mutations.

Changes in chromosomes or genes can be detected with genetic testing. Your doctor or genetic counselor may order genetic testing if they suspect 1 of these changes is causing a health problem.

Learn more about the types of genetic testing: 

Karyotype test 

A karyotype is a picture of a person’s chromosomes. This test can find:

• Large, missing pieces of chromosomes
• Extra pieces of chromosomes
• Pieces of chromosomes that are out of their normal order
• Missing or extra whole chromosomes

Fluorescence in situ hybridization test (FISH test) 

Some changes in chromosomes are too small to see with a karyotype test. FISH testing uses colorful markers that light up brightly under a microscope. The markers stick to specific areas of the chromosomes so they can be seen and studied better. A FISH test does not look at all the chromosomes as a karyotype does, but rather at a specific area of a single chromosome.

This test can find:

• 1 or more missing chromosomes

• Extra chromosomes

• Chromosomes that are out of their normal order 

SNP chromosome microarray test 

Sometimes, changes in chromosomes can be too small to be detected by other tests that use a microscope. A SNP chromosome microarray test can detect very small changes in all the chromosomes. But this test does not show when chromosome pieces are out of their normal order.

This test can find:

• Missing or extra pieces of chromosomes

• Whether both copies of a chromosome pair were inherited only from 1 parent or both parents

Deletion/duplication test 

If a part of a gene (DNA) is missing, or extra pieces are added to the gene, this can affect how the gene works. Deletion/duplication testing looks for changes within a specific gene. These changes may not be detected with karyotype, FISH, or SNP chromosome microarray testing.

This test can find:

• Very small missing or extra pieces of DNA
  

Methylation analysis test 

People inherit 1 copy of each gene from their mother and 1 copy from their father. Usually, these genes both work the same way. They are “turned on” or “turned off” by the attachment of a small methyl group that acts like a switch. 

Genes are turned on or off depending on the type of cell they are in and the activities of that cell. Genes may also be turned on or off depending on which parent they came from. Some genes are always off when inherited from the mother. Others are always off when inherited from the father.

This test can find:

• If specific areas of a certain chromosome have genes turned on or off 

• If copies or pieces of chromosomes were inherited from a single parent, rather than from each parent

Testing for uniparental disomy (UPD) 

Usually, a person inherits 1 copy of each chromosome from their mother and 1 copy of each chromosome from their father. But sometimes, a person can inherit 2 copies of a whole chromosome or 2 copies of just a part of a chromosome from only 1 parent. In that case, they did not get any copies from their other parent as they normally would. This is called uniparental disomy, or UPD.

Scientists can use methylation analysis and/or SNP chromosome microarray to find UPD on a specific chromosome or chromosome area.

DNA sequencing test 

DNA is found inside all cells of the body. It is made of special molecules, called nucleotides, which act as building blocks of DNA. The building blocks are given certain letters. When the blocks come together in a specific order or code, they form short pieces of DNA called genes. Genes carry instructions for cells and can control things like a person’s eye color.

The DNA sequencing test reads the code of DNA letters that make up the genes. It looks for changes from the normal code. These changes are called mutations. DNA sequencing can be done on 1 or more genes. When all your genes are tested at once, this is called whole-genome sequencing.

This test can find:

• If there was a change in the order of DNA letters that make up 1 or more genes
• Which DNA letters were lost or if extra letters were added

Usually, this test does not show larger areas of DNA that are missing, extra, or out of the normal order.

Learn more