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The power of genetics
Who will my child look like? This is the question that all parents ask themselves as soon as they have a positive pregnancy test. Impossible to know in advance the physical characteristics that a child will inherit from his father or his mother. But necessarily he will resemble both in something. The genetic information of each individual is determined by the genes which are contained in the chromosomes. It is through them that the physical characteristics are transmitted. However, living conditions and the environment can modify certain characteristics. For example, the skin is more or less dark depending on whether or not you are exposed to the sun.
The great lottery of heredity
It all starts at the time of fertilization. The sperm fuses with the egg to create an egg. The first cell of a new human being is born. This one receives half of the inheritance of the father and half of the inheritance of the mother (23 chromosomes of one and 23 chromosomes of the other). This does not mean that the child will look half like his father and half like his mother, the laws of heredity are much more complex. Each gene is present in two copies (the alleles). Not all alleles are expressed. Some dominate the others and impose their characteristic as regards the hereditary characters. A multitude of combinations is therefore possible.
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In this picture, lots of info on heredity!
The color of the eyes and the hair… how is it transmitted?
>> Eye color mainly depends on alleles. If the child receives the same two blue alleles, he will have blue eyes. But if he receives two distinct alleles (blue and brown), there is a good chance that he has brown eyes because the brown allele is dominant over the blue allele (recessive). For a recessive allele to be visible, the person must have two.
But all is not so simple. It is possible (the probability is remote) that a child inherits the color blue while his parents have brown eyes. In this case, the parents each have two different alleles (blue and brown): they are said to be heterozygous. Thus, they can pass on a blue allele to their child.
>> What about the hair? It is the same mechanism as for the eyes. Hair color and density depend on genetic information contained in the alleles. The brown allele dominates the blond and the red. So, to have a blond baby, two blond (recessive) alleles must be expressed (beware, early childhood blondness, which fades over years, is not a genetic trait). Regarding the shape of the hair, thick curly hair correspond to a dominant allele, while the thin and smooth come from a recessive allele.
Skin color, a genetic inheritance
>> Several genes are involved in skin color. These will determine in particular the production and distribution of a brown pigment called melanin. The greater the amount of melanin contained in the cells, the darker the color of the skin. A couple who have black skin will have children of the same skin color. But in a mixed couple, the children will have a variable mix. By a lottery effect, some may thus have very dark skin and others lighter skin.
What about genetic mutations?
A mutation is an error in the transmission of genes. Albinism is, for example, a hereditary disease which corresponds to a defect in melanin synthesis. People with albinism have very white skin and very light eyes. We also speak of genetic mutation to explain certain spectacular phenomena such as when two black parents, without white ancestors in their family, have a little blonde girl with blue eyes. Or vice versa …
The blood group and forms the ears: it is also hereditary!
> The earlobe. Its transmission is also genetic. The earlobe exists in two forms: either it is detached of the face, or free (dominant genetic trait), or there is attached (recessive genetic character).
> The blood group. It is transmitted in a hereditary way, according to the laws of classical genetics. It depends on the expression of a gene, says ABO. A baby inherits a gene from each of its parents, which gives the following possibilities: AA, BO, AB, OO, BB, AO. The A and B genes are dominant (or “co-dominant” for A and B), the O gene is recessive.
Other blood groups exist: the system Rhesus, the system Kell… Their transmission to children is also genetic, according to complex processes.
“The top of the face is me, the bottom is his father ! » Mégane, 21 years old, mother of Aliyah, 1 month old
“Aliyah’s hair implantation is exactly the same as mine: the resemblance is striking, especially with the photos of me as a baby. She draws a heart on the forehead. Me again, the shape of the eyes and their color, brown, their distance and that of the eyebrows. In short, I gave her the top of her face, up to her upper lip! Below, that is to say the lower lip and chin, is her daddy, from whom she also borrowed the length of her fingers. “