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“At any given moment, you have the power to say: This is not how the story is going to end.” – Christine Mason Miller

In 2013 Angelina Jolie had her breasts removed after she found out she had a breast cancer gene called BRAC1. The New York Times reported that BRAC1 gave her an 87% chance of getting breast cancer. Our news feeds are stuffed with articles about genes. Half of them report that genes cause diseases and the other half suggest that some genetic drug might cure them. Because this seems to make sense, the US government spent over 3 billion dollars on the Human Genome Project between 1984 and 2003. The Project promised to find the genes for common diseases, like cancer and Alzheimer’s, and eventually cure them.


Reading about genes got me thinking about chocolate cake. I like chocolate cake and I’ve liked sweet things since I was a kid. I have a hard time cutting out chocolate cake. I complained to my friend about this problem and she said I must have a sweet-tooth gene. If that’s right, then I might not be able to stop craving the stuff. Maybe I should give up trying.


I did some research and it turns out that genes don’t tell us as much about us as the newspaper headlines might lead us to believe. Here are five facts about genes that may surprise you.

  1. Humans have about 20,000 That is more than most living things because we are more complicated. But the nematode worm, a tiny species about 1 millimeter long, has as many genes as us.
  2. All the cells in your body have pretty much the same genes. Your hair cells, your heart, your skin, and your bone cells share the same genes, yet they are all very different.
  3. Red blood cells don’t even have any genes (they don’t have a nucleus), and you can remove genes from some cells and they still behave normally for a long time.
  4. Until recently, scientists thought that 2% of human genes were responsible for doing things, with the other 98% of genes being classified as ‘junk DNA’. Now scientists are discovering that ‘junk DNA’ seems to regulate other genes but it is still a bit of a mystery.
  5. A study of 30 men deemed to be at a high genetic risk of developing prostate cancer changed the way their genes were expressed when they followed a strict lifestyle and diet program.


These facts all point in one direction: genes don’t tell the whole story, because environment is important too. This is common sense: if someone has tall genes, but they are malnourished, they won’t get very tall. On average the influence of genes and the environment is equal: our bodies and personalities are 50% genes and 50% environment. It should be no surprise, therefore, that the Human Genome Project is often regarded as a huge flop, because it has not led to cures for common diseases. The new science of epigenetics is starting to explain how the environment even influences what kind of genes we pass on to our children.



Does this mean Angelina Jolie was wrong to have a mastectomy? Not at all. Her mother died of cancer, and her desire to protect herself was completely understandable. Cancer is horrible, and the way people deal with it is personal. Angelina and everyone else’s decisions need to be supported and respected 100%. But we need to base our decisions on evidence. Unfortunately there isn’t much evidence to support benefits of genetic medicine and good evidence in genetic medicine is rare. In the case of BRAC1, best evidence suggests that it increases the risk of breast cancer by 60% not 87%. 60% may still be too high of a risk for many people to live with comfortably, but the decision about what kinds of risks we want to live with need to be based on facts.

What about genes for less serious things like craving chocolate cake? Scientists haven’t yet discovered a sweet-tooth gene, but even if we find one it won’t be the whole story. At best my genes are partly responsible for me loving chocolate cake, but they can’t make me eat it. So there is still hope, and I make a pledge: tomorrow I’ll cut down on chocolate cake. Today I might have half a slice.