DNA is wound up tightly, like a spring, into packets called chromosomes. The average person has 46 chromosomes coupled into 23 pairs. We get one pair from our mom and one from our dad. The code is read three letters at a time and the order of these letters determines the recipe. The final product of a gene is a protein.
Proteins are the basic building blocks of the human body.
They control its growth, development, and normal function. When one letter within a gene changes or if letters are missing, this can affect how the body functions. Using the example above, if instructions for a recipe are changed, this can result in a much different final product. Changes in the code of a gene can cause a protein to be made improperly or not to be made at all. The most commonly altered genes are MSH2 and MLH1.