LOS ANGELES - By opting for surgery to remove her breasts while they were still healthy, Angelina Jolie joined a growing number of women who have used genetic testing to take control of their health.

Here are answers to some common questions about how DNA influences breast cancer risk and what women can do about it.

Question: What genes are involved in breast cancer?

Answer: The two primary ones are known as BRCA1 and BRCA2. Hundreds of variants of these genes have been found that make a woman - or a man - more likely to develop breast cancer. The mutations can increase one's lifetime risk of breast cancer from about 50 percent to more than 85 percent, said Rebecca Nagy, president of the National Society of Genetic Counselors.

In her essay in The New York Times, Jolie said her doctors believed the mutation found in her BRCA1 gene raised her chance of developing the disease to 87 percent.

Scientists know of variants in other genes that also play a role in breast cancer, but these occur more rarely than the BRCA mutations, said Nagy, who works at Ohio State University's James Cancer Hospital in Columbus.

Q: How many people have these mutations?

A: Everyone has the BRCA1 and BRCA2 genes, but only about 1 in 600 women have variants known to increase the risk of breast cancer, said Ellen Matloff, director of cancer genetic counseling at the Yale Cancer Center in New Haven, Conn.

The variants are more common in certain groups of people, including Jews from Europe, and are also linked to ovarian cancer in women. BRCA2 mutations, additionally, are associated with an increased risk of pancreatic cancer, Matloff said. Other cancers have also been linked to mutations in the two genes.

Q: Should I get tested?

A: At the Yale Cancer Center, genetic counselors only recommend testing for people who have a strong family history of a type of cancer that is known to be linked to these genes: breast cancer before the age of 45, several family members with the disease on the same side of the family, breast cancer and ovarian or pancreatic cancer on the same side of the family, a family history of male breast cancer, or Jewish ancestry combined with even one case of breast or ovarian cancer in the family.

Q: How does the test work?

A: The test involves collecting a sample of blood or saliva and sending it to a company that performs the analysis and can deliver a report on which variants you have and how much these variants increase your risk of various types of cancer.

Q: If the test says I have a high risk of breast cancer, should I have my breasts removed?

A: Nagy said that studies have estimated that at least 35 percent of women who have a dangerous BRCA mutation decide to get the surgery when they are still healthy. Doing so can reduce their lifetime risk of breast cancer to less than 5 percent.

Q: Why doesn't it reduce the risk to 0 percent?

A: Even after a double mastectomy, some breast cells remain - and there is always a chance that cancer could develop, Matloff said. However, a risk of less than 5 percent is much lower than the 12 percent to 13 percent risk faced by a typical woman.