Which DNA tests do I need?
The human body is composed of trillions of cells, and each cell has a nucleus. Inside that nucleus are 23 pairs of chromosomes that contain genes. They are made up of DNA (deoxyribonucleic acid) that contains information on how to organize and maintain an organism. Each person has two copies of a given gene, one inherited from each parent. Variations of a given gene are called alleles. There are genes that govern eye color, for example – and different alleles or variations determine whether somebody has brown or blue eyes.
Which DNA tests do I need? It depends on what the DNA test is used for?
The first DNA tests were developed in the 1980s, and they have a multitude of uses:
• Paternity testing, in which the geneticist looks for matches between a child and a possible father
• Ancestry testing is similar: Samples taken from two or more individuals are tested for similarities that could indicate relationship. It’s even possible to determine what ethnic group or groups someone belongs to.
• Genetic disorder testing, in which geneticists look for a mutation or change in a gene that can cause or increase the risk of a given condition. The geneticist can also identify family members who share or might develop the disorder
• Carrier testing is similar. It identifies people who have genes that can cause a disorder, but don’t have any symptoms themselves. Such people can pass the defective genes to their children, and if they marry somebody with the same defective genes, their children could have the full-blown disorder.
• A preimplantation DNA test or PGD is performed when a couple is undergoing in vitro fertilization (IVF). That’s the procedure done to make a “test tube baby,” and involves collecting eggs and sperm from the parents and combining them in a lab. A PGD is then done to determine if any of the embryos thus made have genetic disorders.
• DNA tests are also used for crime scene investigations. The police collect blood, saliva or hair samples, and geneticists can use the samples to try to identify a victim or suspect.
Which DNA tests do I need? How is DNA testing done?
Regardless of the reason for getting a DNA test, the methods of performing one will depend on what the geneticist is looking for. The geneticist will always need a sample of the subject that contains their DNA. Samples usually come from the subject’s saliva, blood, skin or inside of their cheek.
After collecting the sample, the geneticist may choose from any of hundreds of genetic tests to use. The tests fall into several broad categories. In chromosomal tests, the geneticist studies whole chromosomes or long chains of DNA to seek major abnormalities like an extra chromosome. In molecular genetic tests, the geneticist studies single genes or short lengths of DNA. In a biochemical genetic test, the geneticist examines the proteins that make up a given gene.