The color of your eyes depends on the genes that you inherited from your parents. A study found that all humans that have blue eyes share a common ancestor. Recently, a scientist found a way to change brown eyes into blue eyes. That group will have blue eyes, but won’t share the common ancestor with the people who were born with blue eyes.
Your eye color is something that is genetically determined. Blue eyes are a recessive trait. Brown eyes are a dominant trait. You can use a Punnett Square to predict the probability that an offspring of two particular parents will inherit a specific gene combination.
Each parent gives one gene for eye color to their baby. One gene comes from the mother, and one gene comes from the father. This gives every human two genes that express eye color. If both the mom and the dad have blue eyes, then they can only pass on a gene for blue eyes to their children. There is a 100% probability that every offspring of blue eyed parents will have blue eyes.
If both parents have brown eyes, (and each only carries the genes for brown eyes), then 100% of their offspring will have brown eyes. However, if each parent carries one dominant gene for brown eyes, and one recessive gene for blue eyes, then there is a 25% probability that they will produce an offspring who has blue eyes.
Last year, a research team at the University of Copenhagen found that there was a genetic mutation that occurred between 6,000 to 10,000 years ago. Previous to that mutation, all humans had brown eyes. The mutation is what caused some humans to have blue eyes. In short, this means that all humans who have blue eyes share a common ancestor. The mutation causes the pigment in a person’s eyes to be diluted, by “switching off” the production of melanin in a person’s eyes.
Genealogists can look at a person’s eye color and immediately know if that person is a descendant of the common ancestor who first had the mutation that causes blue eyes, or, if that person is not a descendant of that individual.
Genealogists may also look at the eye color of an ancestor in order to attempt to figure out who that person’s parents were. This could be used to help decide upon which ancestor to spend time researching next, in order to fill in more of one’s family tree.
A California scientist named Dr. Gregg Homer has created an experimental procedure that can permanently change the color of a person’s eyes. This procedure uses a specially designed laser to destroy the brown pigment in a person’s eyes. The result is that the person’s eyes will become blue. Essentially, it uses a laser to do what previously could only be done if a person was born with the genetic mutation that causes blue eye color.
If this procedure becomes popular, it will alter some aspects of genealogy. One will no longer be able to assume that a person with blue eyes truly is someone who has descended from the common ancestor that first passed on the genetic mutation that causes blue eyes.
Future generations of genealogists won’t be able to use Punnett Squares to help determine the probability that a person is the genetic offspring of a particular ancestor, either. Maybe they have blue eyes because their parents carried those genes. Or, they might have decided to make their brown eyes blue, (without having the corresponding genetics that cause it).
Image by Dottie Mae on Flickr