How do I explain my eye color

Inheritance of eye color

We will deal with the inheritance of eye color in humans in this article. It explains how the color of the eyes is transferred from parents to children. This article belongs to our biology / genetics section.

The mother has blue eyes, the father has brown eyes. What color of eyes will the child now have? That is exactly what we are dealing with in this article. First, let's take a look at a very simple model for predicting eye color. Unfortunately, biologists have found out that in reality it is not that easy with inheritance of eye color. For schools, however, the simplified representation is sometimes sufficient. Still, let's take a look at both models here.

Definition of the term allele: The individual genetic make-up for a certain trait is called a gene. The functional form of a gene - i.e. the way in which a gene expresses a characteristic is called an allele. The alleles of a gene bring about the expression of the same characteristic in a living being, for example the color (in a flower). However, this feature can present itself in different ways, for example in the form of red or yellow flowers. Multiple alleles are used when there are more than two alleles of a gene.


Davenport model (simplified representation)

The Davenport Model is the easiest to explain eye color inheritance, but it has some weaknesses. Since it still helps with basic understanding, it should be listed here first. According to this model, there is only one gene that determines the eye color brown or blue. This gene is diploid (ie in two “copies”). In the Davenport model, there are two expressions for each copy, namely one for blue eyes and one allele for brown eyes. For example, if the father has two brown eye color alleles and the mother has two blue eye color alleles, the child will receive one brown and one blue allele.

In the Davenport model, the eye color that humans later have depends on which allele is dominant and which is recessive. The following applies: brown eyes are dominant, blue eyes recessive. That is, in the example above, the child would have brown eyes. In a further generation, however, both genes can be passed on equally. If the above child becomes the father whose wife also has brown eyes (with one blue and one brown allele), the probability is at least 25% that a blue-eyed child will develop who has two blue genes and cannot pass on any brown genes. Another 75% of the child will have brown eyes. However, the probability that one of the alleles is blue will still be 50%.


More recent model for eye color

The Davenport model described is now considered obsolete. In reality, the inheritance of the eye colors brown, green and blue is controlled by more than one gene. The function of the genes “bey2” (abbreviation for brown eye 2) and “gey” (green eye) is considered to be guaranteed. For the gene bey2 there are alleles for brown and blue eyes, for the gene gey there are alleles for green and blue eyes. The following order of dominance applies: From top to bottom, dominance decreases and recessivity increases.

So brown is the "most dominant" and blue is the "most recessive". Each of these genes is diploid. In this way, as in the simplified Davenport model described above, recessive genes can be passed on to the child generation, even if these genes do not determine the phenotype (i.e. the external appearance) in the parent generation.
One assumes the effect of other genes that influence the different shades of the colors and control the expression (i.e. the reading out) of the other genes involved, since the genes "bey2" and "gey" outlined above do not explain all inheritance cases either. The case of brown-eyed children in parents with blue or green eyes beyond the genes described above is explained (a) by mutations in the male germ line, (b) by the effect of other (possibly regulating) genes and (c) by the complexity of the Melanin production.


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