There are no defined methods to predict eye color. However, there are some steps you can take to predict the color of your baby's eyes. The first thing you should do is observe the color of the parents' eyes. You can increase the accuracy of your prediction by also considering the eye color of the four grandparents. Once you gather all of this information, you can determine the probability of each color. Since eye color is polygenic (controlled by multiple genes), you should be aware that your predictions might turn out to be a bit inaccurate.
Part 1 of 3: Collect the Eye Colors of Relatives
Step 1. Observe the color of the mother's eyes
Babies inherit genes from both the mother and father to determine the color of their eyes. This means that the mother's eye color has a direct influence on the baby's eye color, although it may not be the same. The first step to a good prediction is to take note of the mother's eye color. You can take one of the following colors as an example:
Step 2. Take into account the color of the father's eyes
Because only 50% of the genes that determine eye color come from the mother, the color of the father's eyes must also be taken into account. Again, the baby's eye color could be different from one or both parents. However, if you know the colors of the parents' eyes, you will have a starting point. Mark daddy's eye color as brown, blue, green, or honey.
Step 3. Find out about the eye colors of the four grandparents
This information is most useful when the grandparents on both sides have different colored eyes. By comparing eye colors, you can learn more about the genes that your children (including one of the baby's parents) have.
Step 4. Observe the eye color of the siblings of both parents
Siblings of parents can also shed light on the variety of genes within the family. When siblings have different eye colors, this may indicate that the parents carry two different genes for eye color (heterozygous) rather than two copies of the same gene (homozygous). This information can help you determine whether the baby's parents are heterozygous or homozygous and increase the accuracy of your prediction.
Part 2 of 3: Consider Other Factors
Step 1. Learn the difference between heterozygous and homozygous
If a parent is homozygous for the genes that determine the color of their eyes, this means that they have two copies of the same allele. If a parent is heterozygous for their eye color, then they have two different alleles for that gene. The most dominant allele is the one that will end up manifesting (the color of the eyes that you will observe).
An allele is a variant form of a gene, and alleles are found in the same place on a chromosome
Step 2. Take into account any additional information you may obtain
The objective of analyzing other members of the family is to try to distinguish whether the parents are homozygous or heterozygous. If a father is homozygous, there is a 100% chance that he will pass the gene for eye color to the baby. However, this drops to 50% for a particular gene if the parent is heterozygous.
- For example, blue eyes indicate a homozygous parent because the gene that manifests this eye color is considered a recessive gene.
- Brown eyes can be homozygous or heterozygous, since the gene that manifests this eye color is considered a dominant gene.
Step 3. Keep in mind that eye color is polygenic
Polygenic traits depend on more than one gene for their manifestation. This means that several genes influence eye color, making predictions based on parental eye color even less certain. However, this information is still a good starting point for an informed prediction.
For example, if both parents have blue eyes, they will both pass a blue-eyed gene to the baby. This means that, in the vast majority of cases, that baby will have blue eyes. However, in rare cases, other genes can change eye color from blue to brown, honey, or green
Part 3 of 3: Calculate Eye Color Odds
Step 1. List all the known genes for eye color
Once you have analyzed all the family members you plan to include, you should make a list of their eye colors. You can analyze this list by hand (or with a computer program) to determine the possible eye colors the baby might have. If you have no experience with inherited genes, you should use a computer program or consult with someone who has knowledge of how genes are passed on. For example, you can make a list like the following:
- Father: blue eyes
- Mother: brown eyes
- Paternal grandmother: brown eyes
- Paternal grandfather: blue eyes
- Maternal grandmother: brown eyes
- Maternal grandfather: blue eyes
Step 2. Search for a calculator on the Internet
These calculators do most of the biological calculations for you. You must enter the eye color of each relative (for example, parents, grandparents, aunts, uncles) in the fields provided. When you're done, the program will analyze the data and tell you the probability of each eye color.
Step 3. Draw a Punnett square
You can use this method to determine eye color by drawing a chart with three columns and three rows. In the first column (the one on the left), you should list the alleles (genes) of the father for eye color. In the first (top) row, you need to list the mother alleles for eye color.
If you can determine the two genes each parent has, you can draw a Punnett square. This procedure will be easier for you if both parents are homozygous. This chart will show you the possible gene combinations for your baby, which will indicate the possible eye colors he will have. Also, the Punnett square will show you the probability of each color
Step 4. Complete the Punnett square
You should find four blanks to the right of the father's alleles and below the mother's alleles. In each space, you should write the father's allele from the left and the mother's allele from the top. These four make up the possible gene combinations for your baby.
Step 5. Determine the probability of different eye colors
The four boxes represent possible allele combinations. Each box represents a 25% chance that your baby has that combination of alleles and therefore the eye color it represents. If a certain combination does not appear in any box, there is no chance of obtaining that combination. If a combination appears more than once, the probability that the baby carries these alleles is higher.