How does DNA change?
DNA copies itself
In order for our bodies to grow, cells must divide and make new cells. Each time a cell makes new cells, the DNA has to copy itself for the new cell. This process is called “replication.”
DNA “typos” cause variation
Any time DNA is copied, a mistake or change can occur in the letters of the DNA sequence, or gene. These changes result in variations or differences in DNA from person to person. Most often, this change does not have an effect because it is like a harmless typo—such as a word misspelled—that is small enough that the sentence still makes sense.
The effects of DNA variation
Sometimes, though, this variation changes the meaning of the DNA instructions and the result is a protein may not be made right. This is like a typo within a sentence that causes the sentence to not make sense. Perhaps several words are missing or two sentences got mixed together. In this case, the protein would not work properly.
Variation can be good, neutral, or bad
Changes in instructions (that is, DNA variation) are responsible for many of the differences (such as eye or hair color, height, etc.) we see between individuals. Variations can be good and cause better-than-normal eyesight, for example. Or they can be harmful and cause birth defects or other health problems.