Deep in the DNA of Marietta Drucker sits one mutated gene amid the tens of thousands that account for, among other things, her blue eyes, blond hair and wide toothy smile.
That gene, one of only a handful of recognizable landmarks in the chemically complex and shadowy map of the human genome has a name, BRCA, and a destiny -- to spawn a potentially deadly form of breast or ovarian cancer.
Six years ago Drucker, then 76, was diagnosed with stage three ovarian cancer, news she believed was a "death sentence" and "about as bad as it could get."
"But then," she says, "it got worse."
Within weeks of Drucker's diagnosis, her two daughters tested positive for the breast cancer gene, an inadvertent and unwelcome gift from their mother.
"I felt devastated. I felt sick about it. How could I give the people most precious to me in my whole life -- my two daughters -- this awful, awful gene," says Drucker, now cancer free after surgery and chemotherapy, from her home in St. Petersburg, Fla.
Rationally, Drucker knows she cannot be blamed for her daughters' cancer and surgeries.
Emotionally, she says, it does not matter.
"The guilt is with me every day. I absolutely blame myself. I was and I still am beside myself that my girls had to go through this hell, that they should have to go through life being worried," she says.
Guilt, evolutionary psychologists believe, is an emotion as old as human societies. It is a "negative emotion," which nevertheless often compels us to altruistic action, allowing us to empathize with and then help those in need.
But it can also be debilitating, filling people with a deep sense of shame that shuts them off from others.
"Our guilt mechanism did not develop at a time when we had a scientific understanding of disease or genetics," says John Tooby, co-director of the Center for Evolutionary Psychology at the University of California at Santa Barbara, who studies how humans developed a guilt instinct.
"We rationally understand we are not to blame, but the guilt mechanism does not," he says. "It's comparable to the way you might be paralyzed by fear when on a cliff, even though you rationally understand you have to climb down to safety."
In families stricken with genetic diseases, feelings of guilt -- even the fear of potential guilt -- plays out in myriad ways. Guilt sometimes prods healthy family members to get their sick relatives treatment, and sometimes causes them to withdraw and distance themselves.
It is not just parents who feel guilty about inherited diseases. Healthy siblings often feel intense shame and self-loathing that they were spared the degenerative or deadly disorder that affected a brother or sister.
Expectant parents who learn their unborn child is sick confront feelings of guilt whether they decide to have the child or abort. And adult children diagnosed with inherited diseases are often reluctant to tell their parents in fear of the guilt they might feel knowing they have upset a parent.
Understanding guilt as it applies to families with genetic diseases is also helping researchers better understand the emotion, which has classically been explained as an internalized sense of morality.
"Psychoanalytically, we look at guilt as an internal process of punishment. You've done something bad, and your superego says you have done something bad and need to be punished. It is an internal way of keeping us moral," says Dr. Philip R. Muskin, a psychiatry professor at Columbia University.
"Guilt can be warranted when you've really done something wrong, but you can also feel it without having done anything," he says.
Advances in medicine have only intensified potential feelings of guilt surrounding inherited diseases. Illnesses that were once chalked up to God's will or a combination of factors can, in some cases, be absolutely attributed to a single bad gene inherited from one parent.
Huntington's disease, a degenerative illness that causes certain nerves in the brain to waste away and results in uncontrolled movements and mental deterioration, is caused by a single defective gene.
If one parent has the gene, there is a 50 percent chance the child will have the defect. Everyone who has the gene eventually develops Huntington's, but because the symptoms do not develop until middle age, parents often do not know they have passed down the disease.
With Huntington's, either parent may have passed down the gene, but in some cases like the degenerative eye disease retinoschisis, which is passed only from unaffected mothers to their sons, there is no question whose genes are responsible and who must shoulder the guilt.
"It is common for parents to feel this is my fault, and in the strictest sense it is their fault. In the strictest sense of who is to blame, the mother is at fault," Muskin says.
"But should she feel guilty? No, though many people in those circumstances would feel guilty," he says.
Because feeling guilty about a genetic disease is an irrational feeling, the best thing to do is think about it rationally through talking with friends, family, a psychologist or a religious adviser, Muskin says.
"A parent can't control the fact that her child has a disease, but she can emotionally take on the burden. Feeling guilty is a sly, emotional way to take control. Ideally, the parent comes to the conclusion that 'this isn't my fault' and accepts there are things out of our control. Can people reach that point? They can. Is it easy? No," he says.
Parents are not the only ones subject to feelings of guilt. Healthy siblings, too, report feeling ashamed that they were spared illness. Siblings feel guilty because they were embarrassed about a sick sibling or because they blame themselves for not doing enough to help.
"My wish was to go to the hospital where my brother was being treated and change places with him so he could be free," says Jay Neugeboren, an accomplished writer and advocate for the mentally ill who has been his brother Robert's caretaker for nearly 50 years.
"I felt I was unworthy. Robert was pure, noble and good and was being punished for being a better person than I was. I was succeeding in the world because I was selfish and he was punished for being loving," Jay Neugeboren says of Robert, who has schizophrenia.
Neugeboren says it took years of therapy for him to stop feeling guilty about his brother's illness and coming to accept that he was not to blame.
"The mantra I came up with and tell people is: 'If I clip my wings, it doesn't help my brother to fly,'" he says.
With the help of her family -- the very daughters who tested positive for the BRCA gene -- Marietta Drucker also came to terms with her guilt.
"As a mother, I understood why she was feeling so guilty," says Drucker's daughter Debbie Sokolov, a cancer survivor who after she was diagnosed with breast cancer began to speak out publicly with her mother about BRCA screening while working for Facing Our Risk of Cancer Empowered, a nonprofit that focuses on people affected by hereditary breast and ovarian cancer.
"But what's amazing, what we kept telling her, is that she saved our lives," Sokolov says. "Knowing I had the gene meant I was able to make the right decisions. She has nothing to feel bad about. I'm alive today because of her. She's my hero."