Due to the recent mapping of the human genome, we now have the ability to have a genetic test done to predict our risk of future diseases. Generally this type of genetic testing is done if a person has a family history of a certain disease and is also done to determine if a fetus has any particular genetic diseases. One could see how knowing this information might be beneficial. If you know you are predisposed to brain cancer you might be more likely to get regular screenings to catch it early. If a mother knows her unborn child has Down syndrome she can better prepare herself for what life will be like when the child is born.
There are some ethical issues to genetic testing. Insurance companies may discriminate against individuals who discover they are predisposed to a certain disease. Also, If one family member finds out they have a high risk of a genetic disease it may affect their entire family since the disease is hereditary.
So while genetic testing is a large breakthrough in science and has some benefits, there are also some ethical issues that go along with it.
Down Syndrome(Trisomy 21): Three copies of chromosome 21.