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Predicting a Child’s Eye Color Based on Genetic Data
For expecting parents, envisioning what their baby will look like is an exciting part of the pre-birth journey. Factors like eye color, hair color, and other physical features remain a mystery until the child is born (and can even change after birth).
However, there are ways to determine the probability of a child’s eye color, using their mother and father’s genetics. In this post, we will discuss how a person’s eye color is determined and provide examples of specific eye color outcomes for children based on their parents’ genetic traits.
How is eye color determined?
In broad terms, a person’s genetics are the determining factor in their eye color. However, the specific genes that affect eye color are more complex than some may realize. Here’s how the process works.
First, these genes produce the pigment known as melanin (which also plays a role in a person’s skin and hair color). The amount of melanin that someone has in the front layers of their iris will dictate what their eye color is. More melanin equates to darker eyes, while less melanin creates lighter eyes.
In addition to melanin, there are also two subtypes of this pigment present in the eyes: red-yellow pheomelanin and black-brown eumelanin. Depending on how much of these pigments are produced, eyes may appear in shades such as green, hazel, or amber.
So what determines how much melanin is produced? Let’s look at chromosome 15, where two genes play a significant role in pigment production. First, the OCA2 gene produces the P protein, which is present in melanocytes (the cells that create melanin).
Meanwhile, the HERC2 gene contains a strand of DNA that controls the expression within OCA2. As HERC2 reduces expression of OCA2, less melanin is produced (leading to lighter-colored eyes).
Examples of eye color outcomes
Putting all of that information into practical use, how can parents-to-be predict their child’s eye color? While there is no way to be entirely certain about the outcome, genetic data can be applied to come up with an assumption about a baby’s potential eye color.
To do this, parents can create a graph (known as a Punnett square) using each individual’s eye color and family history to get an overview of the possibilities for their child’s eye color. On the graph, each parent will be assigned a sequence of letters based on their eye color and the traditional eye color that others in their family lineage have had.
Here’s a simple example. If the mother has brown eyes and a family history of brown eyes, they could be assigned “BB” on the chart, listed on the horizontal axis. If the father has brown eyes, but most others in his family have had blue eyes, he would be assigned “Bb,” listed on the vertical axis. The result is four squares with four possible combinations – two that would indicate a likelihood of brown eyes (“BB”) and two that offer the possibility of blue eyes (“Bb”). To learn about how to create your own Punnett square, check out this resource, which also offers examples of more complex eye color combinations.
As mentioned earlier, this type of analysis doesn’t guarantee a child’s eye color but instead offers an overview of potential outcomes. It is also important to note that melanin takes some time to permeate a newborn’s eyes, which explains why many babies are born with blue eyes that later change.
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