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Eye Colors and Heredity: How Does It Work?

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Eye color within the same family always raises questions, sometimes debates. If we have already seen in a previous article how our eyes could distinguish and differentiate colors , today we are interested in their own colors.

In other times, we thought that the color of the eyes was related to the soul of the person. Today, of course, we can scientifically explain why and how there are almost as many colors as there are people. And we'll try to find out if heredity has anything to do with this.

Eye color: a matter of genetics


You should know that it is the amount of melanin present in the front part of the iris that gives an eye its color. Melanin is a pigment produced by melanocytes through intracellular organelles called melanosomes . All human beings have the same number of melanocytes.

What varies and differentiates individuals is the amount of melanin in melanosomes and of melanosomes in melanocytes. [= ]


People who have a minimum of melanosomes and a lower amount of melanin will have blue eyes while those with a higher amount will have brown eyes . As for those with green eyes , they are halfway there.

To date, scientists have discovered more than 150 different genes that can influence eye color. =]

What about heredity in all of this?

Due to this large number of genes, the relationship between eye color and heredity appears complex. We can, of course, try to think that by looking at the eyes of two parents, we can determine the color of the eyes of their child.


However, it is not systematic. Indeed, this color is at least controlled by three pairs of genes : two on the pair of chromosomes 15 and one on the pair 19. The same gene has several versions called ' alleles '.

[ =] What we already know:

  • Gen 2 of chromosome 15 has an allele that codes for brown and blue.
  • A second gene, located on chromosome 19 has an allele that codes for blue and green.
  • A third gene, located on chromosome 15, gives the color brown.
  • The brown allele is always dominant over the blue allele.
  • The green allele is dominant over the blue allele but recessive (that is, producing its effect only when it exists on both chromosomes) over the brown allele of chromosome 15.

There is therefore an order , a hierarchy . Here are two examples to explain it:

  • If a person has a brown allele on chromosome 15 while all other alleles code for blue or green, then the person will have brown eyes.
  • If a person has a green allele on chromosome 19 and all the other alleles code for blue or green, then the person will have green eyes. It is interesting to know that in order to have blue eyes, all the alleles must code for blue.


What we do not really know is why there are certain shades (gray, hazelnuts …), or why the color of the eyes can, in some people , appear to be hereditary while some children may have eyes of a totally different color to their parents.

So there is still much to be discovered regarding eye color and 'heredity . Our eyes are far from having delivered all their secrets …

Sources: Futura Sciences , News-Medical.net