Eye Color and Paternity
Eye color is a hereditary trait that is unique to everyone. Like our fingerprints, the shape, appearance and color of our eye are singular characteristics that allow the recognition of a person and for some are representative of our personality.
Where does eye color come from?
​
Eye color is based on a pigment called melanin, a dark pigment that protects against UV rays that is also found in other physical characteristics such as skin and hair.
Variations in the amount of this pigment play a role in the color, from the darkest shades of brown to lighter colors such as blue or green. Thus, lighter colors contain less melanin than darker colors.
​
The concentration and distribution of melanin in the iris, the circular layer that surrounds the pupil, are hereditary processes that develop after birth. Thus, the eyes of newborns are generally blue, and it is only from the age of 3 that the final color of a baby's eyes stabilizes.
The color options are: blue, brown, grey, green and hazelnut. The most common is brown, for about 80% of the world's population. About 8-10% have blue eyes, 5% hazel eyes, and 2% green eyes, making this the rarest color.
Eye color and heredity
By genetic inheritance, the DNA of a child is composed of half of the genes from his father and the other half from his mother . In other words, the genetic profile of a person is the association of 46 chromosomes inherited from the biological parents in a random way.
The chromosomes are ordered in pairs and each pair contains a DNA molecule from the parent. The DNA molecule has segments that can provide specific function to the cells, which are called genes .
​
These genes, which also work in pairs, determine a large number of physical characteristics, including eye color. The genes present in the cells of the iris control the production of melanin which is the dark pigment making eye colour darker .
​
Eye color depends on the combination of 2 major genes inherited from our parents , if we do not take into account the different possibilities of genetic mutations or external factors that can also play a role in the perception of color.
​
- The Br gene, which groups the brown color "B" and blue color "b"
- The Ve gene, which includes the green "V" color and the blue "b" color
​
The Br gene is located on chromosome 15, while the Ve gene is located on chromosome 19.
​
During this combination, there is applied a rule of dominance between the genes playing a role on the observable physical characteristic. Genes that generate large amounts of melanin, creating brown eyes, are therefore dominant over genes that generate lower amounts of melanin, responsible for blue eyes. Recessive genes, like the color blue, are only expressed in the absence of a dominant gene.
​
-
The brown "B" gene is dominant over the green "V" gene and over the blue "b" gene
-
The green "V" gene is dominant over the blue "b" gene
-
The blue "b" gene is recessive to the brown "B" and green "V" genes
​
Thus, when you inherit a brown eye gene, it will naturally dominate over the blue eye genes and therefore you will be more likely to have brown eyes.
How is eye color determined?
The combinations of genes and eye colors!
​
Consider that the genes involved in eye color work in pairs, that they are found on chromosomes 15 & 19 and that they obey the rule of domination - recession.
So there are only 9 possible combinations to define a person's eye color.
Filiation with eye color
It is impossible to determine parentage with precision, by comparing eye colors, but certain dispositions can be taken into account to at least have an idea. We know that the color of the eyes of children is influenced by that of the genes of the family .
​
It's natural in your research to start by comparing the eye color of family members. Observing the eyes of the mother, father, grandparents, uncles, aunts and brothers and sisters makes it possible to draw a first conclusion on the diversity of genes within the family.
If the colors of the eyes are different in them, we could conclude that the genes determining this character are heterozygous, therefore carried by two different alleles instead of being homozygous, carried by two identical alleles.
Homozygous genes
A person is homozygous if the genes that govern eye color are identical in the pair of chromosomes
Heterozygous genes
A person is heterozygous if the genes that govern eye color are different in the pair of chromosomes. In this case, only the dominant gene will express eye color
Can paternity be verified by eye color?
​
It is clearly not possible to confirm a reliable parentage link with only the color of the eyes of a presumed father. Apart from probability calculations that must be taken into account based on family genes, today more than 80 genetic mutations have been identified that are involved in a person's eye color. Thus, it is possible that 15 to 20 additional genes play an indirect role in the expression, concentration and distribution of melanin. And yet, this link is not yet clearly established.
​
The color of the human iris is therefore far from being able to be explained by a single factor, it is also necessary to know that the expression of genes can change during the life of a person, which explains that the color of the eyes can evolve. There are even people who have a condition called heterochromia, a difference in colors between the two eyes, also known as "wall eyes", or within the same iris.
​
Beyond DNA and color changes due to aging, pathologies and treatments can also play a role in color modulations. These can be of inflammatory, traumatic, tumoral, neurological or toxic origin, involved in loss of pigmentation, then can darken the iris.
​
Eye color is a polygenic characteristic. That is, multiple genes are responsible, making a conclusion based on observation alone less likely. Because you must take into account that it is possible to inherit a recessive gene not observable in the parents, but which can bring out a new color in the child.
​
Eye color was attempted to be determined by a color chart, similar to the one pictured below. The idea is to try to calculate the percentage of eye color a child is most likely to have , based on the parent's eye color.
​
The main ideas are mostly true, where parents who exhibit the same eye color are more likely to pass on that same color to children, with brown color dominating over lighter colored eyes.
Can we predict the color of a baby's eyes?
However, it is not the most scientifically accurate way to determine the child's inherited eye color. The truth is that eye color can be affected by several factors which, when taken together, can change the color a person will have.
Can you choose the color of a baby's eyes before birth?
​
Yes, today, it is technically possible to use Medically Assisted Procreation to select the embryos of parents carrying the genetic codes for a desired eye color. This laboratory selection greatly increases the likelihood of a new pregnancy carrying the genetic code for a chosen eye color.
It is nevertheless important to check beforehand whether the parents are carriers of the genetic codes necessary to constitute the desired eye color for the child. Today, a simple blood test is used to check this compatibility. Next, the lab's procedure is then to examine the embryos produced by the parents with in vitro fertilization to determine which of the embryos carries the necessary genes to greatly increase the chances of the desired eye color.
​
After this selection of the embryos according to the criteria, the parents can then choose to implant only the embryos with the greatest probability of obtaining the desired eye color.
Blood group and parentage
Blood type can help determine paternity in conjunction with other tests such as DNA testing.
Blood types are inherited characteristics that can be passed down from one generation to the next.
