DNA technology has advanced to the point where paternity testing can identify a child's father with very little error. When a couple in New York needs to determine paternity, one can compare DNA samples for similarities. DNA fingerprinting is a simple way to determine paternity, and this process involves using a restriction enzyme to cut out some sequences of DNA but not others and then compares the results. When using restriction enzymes to create DNA fragments, what is left of a child's DNA would resemble a combination of two parents' DNA.
All humans have mostly the same DNA that is comprised of four bases referred to by the letters A, C, G and T. Two random people would sometimes have a different base about every thousand bases. Those who are related will share even more bases than one would with a stranger because a child gets half of a mother's and half of a father's DNA. A child's DNA is more than 99.9 percent like a parent's DNA but would also be similar to grandparents or cousins.
If two men were possible fathers of a child, a DNA tester would collect DNA from the two men, the mother of the child and the child. A tester would put each person's DNA fragments on an agarose gel and see which combinations make up the child's DNA.
When a couple is not married or going through a divorce, paternity can become very important. Even one who has helped to raise a child may not receive the same visitation or custody rights a biological parent would. Conversely, a man may have to prove paternity when he never married the mother of a child to gain visitation rights. When paternity is proven, a child's father also has responsibilities and may be ordered to pay child support.
Source: The Tech Museum of Innovation, "Genetic Testing", June 01, 2004