Q. What is genetic testing?
A. Genetic testing is a specialized form of testing that doctors and scientists can perform to determine if there are abnormalities present in a person’s DNA. These abnormalities may signal the presence of a disease or the propensity to contract a disease later in life. The abnormalities discovered through genetic testing can be large or small – from a single gene being altered to whole chromosomes being added or deleted.
Q. Is genetic testing the same as genetic screening?
A. No. Technically, genetic screening is a more narrow term which refers to the detection of genes that may predispose individuals or their descendants to certain diseases. It is performed on populations (or individuals from populations) that are at risk for certain diseases. Genetic testing is a broader term but is similar in that it focuses on detecting genes that may predispose individuals to certain diseases. It differs from genetic screening in that it is generally performed on individuals who do not necessarily belong to high risk populations. However, the terms genetic testing and genetic screening are often used interchangeably. We will use the broader term, genetic testing, to encompass both terms.
Q. Are chromosomal abnormalities the same as genetic mutations?
A. No. Chromosomal abnormalities are irregularities in the number or structure of chromosomes. A change in the chromosomes (either a change in structure or an increase or decrease in the number of chromosomes) results in a loss or gain of genetic material. However, there is usually nothing inherently wrong with the genetic material (DNA) that is contained in the chromosomes. An example of a chromosomal abnormality is Trisomy 21 – also known as Down syndrome. People that are affected have three copies of chromosome 21 instead of the normal two copies.
In contrast, a genetic mutation means that there is a change in the actual DNA sequence (genetic material). In some cases this can lead to a disease state. A person with a genetic disorder caused by a mutation often has a change in just one gene (for example, cystic fibrosis is a single-gene disorder). The consequence of this genetic mutation is that the gene does not properly code for a protein. That protein is then deficient, abnormal, or absent. An improperly made protein can cause many different disorders that may affect the whole person.
Q. What is a karyotype?
A. A karyotype is essentially a photograph of a person’s chromosomes. Karyotypes can help doctors see if a person has a chromosomal abnormality which will result in a condition such as Down syndrome. Karyotypes cannot show us individual genes or genetic mutations.
A karyotype gives individuals a big picture of the number and the appearance of the chromosomes in a human cell whereas genetic testing offers a more detailed look at specific gene sequences. If you look at the karyotype of a person with a genetic disorder, you would not see anything abnormal. However, if you look at an individual with a chromosomal abnormality such as Down syndrome, that abnormality would be represented on the karyotype.
Q. What is Pharmacogenetics?
A. Pharmacogenetics is a specific area of genetic research that uses DNA samples to study how people respond to medications. Specialists in this field, pharmacogeneticists, study drug responses in populations and individuals according to DNA variations. They also identify gene profiles that are associated with drug side effects. Then, a doctor can work toward reducing a patient’s adverse reaction to a drug by personalizing their prescriptions to their individual genome. The goal is to be able to choose appropriate drugs based on the patient’s genetic characteristics.
Q. Does everyone have the same DNA (genetic code)?
A. The genetic material of all humans is 99.99 percent the same. But interestingly, the .01 percent variation in DNA between people accounts for the different characteristics of each person (hair color, skin tone, predisposition toward specific diseases).
Dawn Vargo is an associate analyst for bioethics in the Public Policy Division of Focus on the Family.
Frequently Asked Questions: Genetics
For more information see Jeffre L. Witherly, Glaen P. Perry, and Darryl L. Leja, An A to Z of DNA Science: What Scientists mean when they talk about genes and Genomes, (New York: Cold Springs Harbor Laboratory Press, 2001), p. 70.
If you enjoy reading stories like this one, sign up for the free CitizenLink Daily Update e-mail. You'll get news and commentary from Focus on the Family Action delivered right to your computer.
