DNA is inherited from both biological parents
DNA, also known as deoxyribonucleic acid, is found in all cells of the body. It is composed of four different molecules—adenine (A), thymine (T), cytosine (C), and guanine (G). Like the letters of an alphabet, these four molecules are arranged in strings of specific sequences that spell out instructions for our body’s everyday functions. DNA contains information that dictates our physical characteristics, such as facial features, height, and even health.

During conception, the father’s sperm cell and the mother’s egg cell, each containing half the amount of DNA found in other body cells, meet and fuse to form a fertilized egg, called a zygote. The zygote contains a complete set of DNA molecules, a unique combination of DNA from both parents. This zygote divides and multiplies into an embryo and later, a full human being.

At each stage of development, all the cells forming the body contain the same DNA—half from the father and half from the mother. It is this fact that enables scientists to use a variety of sampling methods for DNA testing. We can take samples at virtually any stage of development and from any part of the body—and still obtain the same results, because these samples contain the same DNA.

Special locations (called loci) in human DNA display predictable inheritance patterns that could be used to determine biological relationships. These locations contain specific DNA sequences, called markers, that forensic and DNA scientists use as identifying marks for individuals. In a routine DNA paternity test, the markers used are Short Tandem Repeats (STRs), short pieces of DNA that occur in different repeat patterns among individuals.

Each person’s DNA contains two copies of these markers—one copy inherited from the father and one from the mother. Within a population, the markers at each person’s DNA location could differ in length and sometimes sequence, depending on the markers inherited from the parents.