Rare parents do not try to imagine what their baby will look like. And dreams sometimes lead them away.
So, the future mom may dream that the girl will certainly have blue eyes, like her father, and blond hair, like her own, but her daughter’s temper should be nice, like Aunt Ani.
If the parents are waiting for the boy, they can mentally order him a manly oval face and a charming dimple on his chin, like a grandfather. But God save the son to inherit his grandfather’s character, because in his youth he was an arrogant daredevil, and he never helped his grandmother around the house.
However, parental expectations do not always come true.
The decisive vote remains for the genes that he will receive from mom and dad. Although the environment will also contribute to this and it is better not to forget about it.
We all know that a new life is born when a spermatozoon meets an egg cell. But few people remember that mother’s and father’s germ cells are called gametes. Both carry 23 chromosomes.
This is their main difference from all other cells of our body, each of which contains 46 chromosomes. A half set of gametes is carried because it was originally created to reunite with each other and form a single cell – a zygote, from which, later on, thanks to the mechanisms of division, a new person will turn out.
For the same reason, the child receives exactly half of the genetic material from the mother, and the second from the father. In total, the zygote will contain the 46 chromosomes laid by evolution.
Those chromosomes that do not differ in men and women and almost completely repeat each other are called autosomals, and those that are responsible for the difference between the sexes, sexually. The first paired, and the second – paired in girls (XX) and unpaired in boys (XY).
Chromosomes are specific structures. They are located in the nucleus of cells.
Inside each of the 46 chromosomes lies one DNA molecule, which carries almost all the genetic information about a particular organism. The chemical formula of deoxyribonucleic acid is quite simple. It consists of only 4 nitrogenous bases, sugar molecules and the residue of phosphoric acid.
The secret is in another.
The shape of the DNA resembles a double stranded helix. If you unwind the spirals of all 46 DNA molecules from a single cell, their total length will be almost 2 meters.
And in this chain all the genetic information fits because it will be written in the form of text of all 4 letters: A, T, G, C (this “alphabet” is made up of the first letters in the name of 4 nitrogenous bases). If you bring together information that carries 46 DNA molecules, you get the text of 3 billion letters.
This is more than any average home library can hold.
But what are genes? These are only DNA fragments that are responsible for the formation of proteins and RNA (ribonucleic acid, which is also involved in the synthesis of proteins). To a non-specialist such functions will seem at least frivolous, while others might think that this is a joke.
However, do not rush to conclusions. As is known, all living organisms, from chamomile to humans, are composed of proteins. Any differences, both external and internal, are provided thanks to a huge variety of proteins that have different structure and different properties.
But since the structure of proteins is encoded by genes, it turns out that they also regulate all the characters we inherit.
At last count, each of us has from 21,000 to 25,000 genes, although, despite the recent deciphering of the human genome, their exact number is still unknown. And the questions after the sensational discovery has not diminished.
Thus, the coding regions of genes constitute only 5% of the total length of 46 DNA molecules. For what are the remaining 95% of “gene fragments”, scientists still can only guess.
Genetic material is transmitted not only from mom and dad. In the creation of the baby, paradoxically, grandparents and even distant relatives take an active part.
How else to explain that a child has a crooked nose, if the parents have an ideal Greek profile? The fact is that a certain set of genes is laid in mama’s and father’s germ cells as a result of random selection even during their maturation.
Thanks to this lottery, a fantastic number of unique gene combinations is achieved.
For the same reason, all the spermatozoa of one man and all the eggs of one woman are not similar to each other, the children of the same married couple are different, and each person on the planet gets their own unique genetic baggage. The only exceptions are identical twins, who are exact genetic copies of each other.
By chance, and solved another equally important task. The evolution of species is provided by mutations – unreasonable and unpredictable changes in hereditary material. To see the result of these metaphors, it is enough to compare the person with the earthworm.
It turns out that we have 250 identical genes with him, which means one common ancestor.
Man became the crown of creation thanks to the ability of all living organisms to respond to changes in environmental factors. And you can only react to them due to mutations. However, this saving mechanism has one unfortunate drawback.
As a result of mutations (in this case, they can be called “breakdowns”), DNA molecules or chromosomes develop hereditary diseases. But this is a payment for moving forward.
All signs for which one gene is responsible are called monogenic. Otherwise, they are called Mendelling because they are inherited according to the laws of Mendel. These signs include: blood type, Rh factor, the presence or absence of a hump on the nose, the presence or absence of hair on the head, the presence or absence of pigment coloring hair and skin (normal pigmentation or albinism), the shape of hair (curly or straight), thickness lips (full or thin) and so on.
The color of eyes, hair and skin is also included in the “monogenic” group, although in reality it is not. Given the rich palette of color shades that arise in practice, we can conclude that not one but several genes are responsible for the realization of these external features.
Nevertheless, the laws of Mendel are best illustrated by the example of eye color. Each gene has one or more alternative forms – alleles.
So, the gene encoding the color of the iris, has an allele that is responsible for brown color, and there is an allele that is responsible for blue color. To simplify the picture, all alternative forms can be divided into “strong” and “weak”. As Mendel found out, the former are responsible for the transmission of dominant (or dominant) traits, the latter for the transmission of recessive (or weakly manifest) traits.
A priori, the cells of the body may contain only two alleles of each gene. We get one from mom, the second from dad. From the combination of alleles and will depend on what sign we show.
In a dispute about the color of the eyes, the form of the gene that is responsible for the careers color of the iris wins. According to the same laws, monogenic hereditary diseases are transmitted to the child.
Signs for the development of which several genes are responsible are commonly called multifactorial. These include the shape of the face and nose, indicators of physical strength, level of intelligence, memory properties, character traits, mathematical or musical talent.
How exactly these signs are realized in the child will depend not only on a certain number of genes and their specific characteristics, but also on external factors. Thus, the level of intelligence will largely determine education, character – education, strength – the presence or absence of training.
Hereditary diseases are conventionally divided into two groups: chromosomal and gene. Genetic diseases, as well as signs, are monogenic and multifactorial (in other words, diseases with a hereditary predisposition).
The latter includes the vast majority of chronic diseases of a person with damage to the cardiovascular, respiratory, endocrine and other systems.
In order for them to manifest in a child, two unpleasant coincidences must happen at once. First, he must learn from his parents a certain number of genes, but then he will inherit the predisposition, not the disease itself. Ailment will be felt only if the influence of the environment turns out to be negative.
Thus, more than 1,500 genes are involved in the development of a hereditary predisposition to bronchial asthma. Even if the baby borrows a complete set, but at the same time will live in a favorable ecological environment, he will not get sick.