Thank you. That's DNA. It is sometimes called the blueprint（ 蓝图） of life. I'm sure we've all heard that before. Well, in some ways it is true. You can't change your eye color, for example, but in many ways it really isn't.

  Our DNA changes every day. DNA is actually getting damaged every day by external（外部的） factors, like UV rays（射线） from the sun, or internal（内的） factors like chemicals. Humans do encode（（将文字材料）译成密码） in their DNA proteins（蛋白质） that can repair that damage, but those processes can't repair everything. For instance（实例）, when you go out into the sun and get exposed（使暴露） to UV without sunscreen, you can get a burn（烧伤）. That is your DNA getting so damaged that it can't be repaired. The protective（保护的） effect is to let those skin cells（细胞） die.

  However, most times your DNA repair can repair that sun damage, but my advice is don't let those proteins work too hard. Mistakes over time can be dangerous. This is best illustrated（(用图等)说明） by some rare diseases where DNA repair proteins（蛋白质） don't work properly. For one of these, a symptom is the onset（开始） of skin cancer（癌症） at the age of 8 years old, nearly 50 years younger than the general US population. This is part of the reason why cancer, a disease of DNA damage that does not get repaired properly, increases with age. The improperly repaired DNA damage causes mutations（变化） in the DNA.

  However, mutations are not all bad. Although mutations can cause cancer in some situations, in other situations, they can also result in beneficial（有益的） evolution（演变）. Mutations formed humans as a species and every other organism on the planet. Organisms evolve（发展） by acquiring（获得） mutations（变化）. But how does biology decide what are good and what are bad mutations? I think of it like this.

  When we encounter（遭遇） uncertainties（无常） in life, it incites（激动） an uncomfortable feeling. One that can result in an attempt（企图） to bring things back to the status（身份） quo. Repair the damage and bring things back to the way they were. However, sometimes inaction is not an option. With some uncertainties, we've just needed to weigh the risks and make the best decision with the information available. We may have had a plan, a blueprint, but at times we've had to throw that out and just wing it.

  Induce（劝诱） those mutations（变化） in our life's blueprint（ 蓝图）. I think we've all been there before. I know I have, maybe too many times. I took a risk near the end of my PhD and I flew all the way from Canada to Australia to go to a conference celebrating the 50th anniversary（ 周年纪念） of the discovery of DNA. All the best people in the DNA repair field were going to be there. And I was convinced during this trip that I was going to find a post-doctoral lab to work in in order to help me answer the question of how mutations occur in DNA despite（不管） DNA repair proteins（蛋白质） and how biology is weighing these risks.

  Luckily, that risk worked out. And some days I still think to myself, how? But that is another story for another time. The important part here is that I did find a professor from the United States to work with who studied exactly what I wanted to work on. And this was how bacteria（细菌） deliberately（ 故意地） introduce mutations（变化） in their DNA. He and others discovered that bacteria lacking the ability to deliberately induce mutations in their DNA grew similar to other bacteria under normal growth conditions.