Well I don't know who Lyndsay is but...the eyes are of different colors due to mosaicisim. Mosaicsm occurs with the existence of cells of two different genetic materials in the same person. Normally, all body cells would have the same number of chromosomes. So in Lyndsay's case the genes for a blue iris were expressed in one eye and the genes for a brown iris were expressed in the other eye. This type of mosaicsm is uncommon in humans but very common in the Australian Shepherd breed of dogs. The IRIS is the part of the eye that gives it color. Eye colors vary from light blue to dark brown, depending upon the amount of pigment called melanin that is contained within the iris. Muscles within the iris cause the pupil to get larger or smaller to control the amount of light that comes into the eye.

The color of our skin, hair, and eyes comes from pigments made by our cells. The program for making pigments (and everything else) is in our DNA. There are several genes in our DNA that tell our cells how to make and deposit pigments into our irises.If they are all "switched on" and have the pigment codes right, our eyes are a very dark brown. If only some genes are "on" and have the right directions, our eyes can be light brown or hazel. If we lack all of the pigment codes or they are shut off completely, we have blue eyes. So there are two things operating, one is the presence or absence of instructions, the other is whether the process is switched on.

Usually both our eyes are the same color. Normally every cell in our body (with two exceptions) has exactly the same DNA. The one cell we each grew from had a specific code that was passed on to each cell that makes us up. Each cell uses only the programs it needs, but it has them all. Sometimes when copies are made, something is not copied exactly, so that the DNA in the new cells is different. This is called a mutation. This means that the DNA in some of your cells will be different from the DNA in other cells. So in the cells of one of Lindsay's irises the directions for making and depositing pigments are probably missing or turned off. Have you seen patches of different colors in coats of animals? Many animals (including people) are born with eyes, hair, and skin that are very light, even if they will later be dark. Sometimes baby animals have very different colors and patterns than adult ones. Why do you think this is?