Eye Color and Genetics.

It is known that just a few "letters" out of the six billion that make up the genetic code are responsible for most of the variation in human eye color. Differences in eye color are largely down to "single nucleotide polymorphisms" (SNPs - pronounced "snips"), i.e. "single letter changes"; variations in the sequence of letters that make up a single strand of human DNA.

SNPs represent a change of just one letter in the genetic sequence. These changes, or mutations, in our DNA can have important consequences for how the gene gets physically expressed. There are two copies (one backup) of 3 billion letters in the human genome. Looking for the letters responsible for human eye color is like looking for one or two needles in the hay. Unforgettable eyes of the Afghan girl on the cover of the National Geographic are couple of variant letters in the human genome. Beauty is hidden in the details.