Boulder Q: Is DNA more easily damaged by industrial chemicals as opposed to UV light exposure?
Like most things in biology, it depends. First, many industrial chemicals are not particularly “genotoxic.” They may be irritants or cause damage some other way, or they may be relatively harmless. Then, it is a question of dose. Many chemicals are known to damage DNA only at much higher doses than are ever achieved in the environment. PCBs are an example; no one is sure if they are harmful at the very low exposures the average person receives. UV is dangerous, but as we’ll see in the Cancer talk, there are many events that have to take place before that sunburn results in a skin cancer. Boulder Q: In multiple births, how common is it for one of the babies to be born with a birth defect (for example, Downs Syndrome) when the other is not? Is this only possible in fraternal births, or is it possible in identical ones as well? Down syndrome is usually caused by the fetus having an extra copy of chromosome 21 in some or all of its cells. The chromosome is normal but the extra copy unbalan
