WHAT IS DNA? DNA is the blueprint that encodes all the data for building a human body, along with instructions for how the body should operate. Every cell in a person's body contains a copy of this code. "DNA typing" is based on an unusual feature found in the human genome. There are multiple copies of certain short sequences, 3 to 30 base pairs long, that are repeated one after another as many as 100 times. These groups of repeat sequences are widely scattered through the genome. Everyone has these repeat units, but the number varies from person to person; only identical twins will have the same numbers and patterns of these sequences. Though these extra units aren't instructions to make anything, scientists think they might exist to provide some variety for evolution.
MATH HELPS CUT CALORIES: A food label that says a product is "90% fat free" will be more appealing than one that says it has "10% fat." People also lend more credence to exact numbers, preferring "50%" to the less specific "half." But it's easy to confuse precision with accuracy, such as with food packaging. Compare a soft drink that has 39 grams of sugar and 140 calories per serving to a fruit drink with 31 grams of sugar and 120 calories. At first glance, it might sound as though the fruit juice is the healthier option. But the serving size of the soft drink is 12 ounces, while the fruit drink is only 8 ounces. So ounce for ounce, the soft drink has fewer calories and less sugar than the juice.