Nature is very capricious at times, and genetics too, so much, that a few days ago I met a couple who had both brown eyes both father and mother whose baby had blue eyes. Well, I said capricious not to call it otherwise, because they told me that they were starting to be a little tired of looks and comments, with greater or lesser grace, related to electricians, plumbers and butane.
It is true that it is very unlikely that two parents with brown eyes have a child with blue eyes, but it is not impossible. Similarly, they may also have children with green eyes and in fact they are more likely to come out green than blue. So if you have brown eyes and your partner too, do not convince yourself still believing that none of your children will have green or blue eyes, why it's possible and now I'm going to explain why.
Open the Natural Sciences books on page 56
I'm sorry, I have to make a little reminder of the Mendel's Laws to explain the subject of the eyes, so cast your mind back to your EGB era, dig into your memories and show me that going to school served you for something more than to warm the chair (it served me for that and for have a new case every September ... little else).
Well, we begin by explaining that Gregor Mendel discovered the basic rules that govern genetic inheritance with several experiments with plants, the most famous being that of peas. Mendel grew green peas and yellow peas. He crossed the two varieties obtaining the following result: 100% of the peas were yellow. Then he took these yellow peas and crossed them between them, obtaining a very curious result: 75% of the peas were yellow and the remaining 25% were green.
In Babies and more The baby's eye colorNot happy to see that all this was very strange, the new generation of peas fertilized, seeing that with the yellows the same thing happened again (75% yellow and 25% green) and that with the greens all green came out, 100%. Thus he realized that there was dominant hereditary characteristics and recessive hereditary characteristics.
We repeat, with an image
Now we explain it again with the image, to see it more graphically. The roughness of the pea is also specified in the drawing, but as we do not need, we will be left with only the first two letters of each type of pea. Yellow is a dominant feature, so it is called TO (uppercase) and green, which is recessive, is called to (lower case). Above all you have a yellow pea (AA) and next to it a green pea (aa). I repeat, look only at the first two letters.
When crossing these peas, Mendel obtained yellow peas, all of them. The reason is that everyone was Aa. When two species come together, one gives one gene and the other from another gene, as you can see, make the combination as you do, it always comes out Aa (the first TO of yellow with the first to of green, the first TO with the second to, the second TO with the first to and the second TO with the second to). Therefore, being all Aa, dominating yellow over green, all are yellow.
Now, when crossing all Aa the unexpected happened because 25% of green peas came out. In the picture I think it is understood quite well. Whenever one of the crossed peas gave a TO capital letter the pea was yellow, however on a quarter of the occasions a Aa yielded his to lowercase and the other Aa also, resulting in a pea aa, that is, green. If then those greens crossed each other, they would undoubtedly always be green because none wore a TO.
Explaining the color of the eyes
The theme of eye color is a bit more complex than peas, because we have two chromosomes guilty of eye color. One of them is the chromosome 15, where there is a gene that influences the color and whose possible alleles are brown and blue. The other is the chromosome 19, which also has a gene that influences color and whose possible alleles are green and blue (that is, we all carry genes of green and / or blue, because on chromosome 19 there is no place for brown).
As with pea colors, there are dominant and other recessive colors. The brown is dominant and whenever it is “will win” the rest, the blue is recessive and the green is halfway, because it is dominated by the brown, but dominates the blue. To make it easy we will call M to brown V to green and to to blue
In Babies and more "Baby Eye Color": an Android application to know the color of eyes your baby will have There are many possible combinations, because as we said there are two chromosomes that give the color of the eyes. A person whose eyes are blue has the easiest combination, aa on chromosome 15 and aa in the 19. Only it was Ma-aa, he would already have brown eyes. If i were Ma-VaI would also have them brown and, if I had them aa-va, I would have them green (then there are many more combinations, of course, because 15 can be MM, Ma, aM or aa and 19 can be VV, Va, aV or aa). Also then you have to keep in mind that more things influence, because there are people who have brown eyes but pulling greenish, there are those who have dark brown, there are people with one eye of each color, etc. But well, to get an idea of the generalities, today's explanations are more than enough.
The key is in the recessive “a” of both genes
To explain how can a couple with brown eyes have a child with blue eyes we have to know, simply, that the key is that both parents have a to on each chromosome If the father is, for example, Ma-Va and the mother is also Ma-Va (both have brown eyes) will have a 75% chance of having children with brown eyes (MM, Ma or A.M on chromosome 15), 18.75% of having green eyes (aa on chromosome 15, and VV, Go or av in 19), and a 6.25% of having blue eyes (aa-aa).
A case with more probability of having children with blue eyes would be if one of the two were Ma-aa and the other Ma-Va and the case of more likely brown-eyed parents would be if a father and a mother got together with the combination Ma-aa Y Ma-aa. In the latter case the probability of having brown eyes on the children would be 75% and to have them blue of the remaining 25%.
So if you ever meet a couple with brown eyes with a baby with blue eyes, know that it's possible. It is true that it is also possible that the child belongs to another, but it is better to trust couples' fidelity, right?
