The secret of human life lies in a filament meter-long and only a few billionth millimeter wide. Of course, you guessed it: this is DNA, or deoxyribonucleic acid. Coiled up, it is placed in the center of the nucleus of each cell in the form of 46 chromosomes, which contain 50–100 thousand genes.
We inherit them from mom and dad in equal parts. Each chromosome has a pair (total pairs 23), except for sex chromosomes in males (unpaired X and Y).
If there are different genes in a pair, only one of them will manifest itself – the dominant one. The “suppressed” gene is called recessive.
In order for a child to manifest a recessive hereditary trait, both mom and dad must simultaneously transmit to their child. But the dominant trait will become apparent, even if the baby gets from only one parent.
For example, for a child to be brown-eyed, one brown-eyed parent is enough: brown is the dominant trait in relation to blue. In fact, of course, everything is more complicated.
Let’s say a baby can get blond hair from a mother, but it will grow like a father’s. It is because of the amazing diversity in the combination and distribution of genes that we are surrounded by completely different people, and brothers and sisters also do not repeat each other.
There is only one chance for billions that non-twin children from the same family will be genetically the same.
Theoretically, the chances of having a boy or a girl are equal for a woman, because the sex of the child is determined by the sperm cell. If the egg is found in a sperm cell with the sex chromosome X, there will be a girl. If the sperm carries the Y chromosome, a boy will be born.
Some studies show that the sex of a child also depends on what day a significant meeting took place regarding the time of ovulation (that is, the appearance of an egg ready for fertilization). Sperm with X chromosome is not as mobile as their Y-brethren, but live longer. So, the closer conception to the day of ovulation, the greater the chance of having a baby.
If the intimate act occurred before or after ovulation, the probability of becoming the girl’s parents is higher.
Blood type depends on which sugar molecule is on the surface of red blood cells (red blood cells). If it belongs to type A, the baby has blood type II, type B has group III, while A and B have group IV.
If there is no sugar molecule at all, I group is obtained. Parents with groups II and III may have a child from any of the four groups.
And mom and dad with the I group – only with exactly the same.
When it comes to these characteristics, one has to consider the influence of dominant and recessive genes. The former are usually “responsible” for darker colors and can suppress the action of genes “responsible” for light shades. For example, a dark-haired father, who has a crooked nose, and a fair-haired mother with a roman profile, most likely, will have a baby that looks like his father.
But surprises are possible. Growth seems to be directly dependent on the genes obtained, and the child will not be a giant for low parents, and Thumbelina is unlikely for a high parent. But with a combination of opposite signs, the baby will inherit either the father’s data, or the mother’s, or it will be somewhere in the middle.
Do not forget about the role of the environment. It is known that each new generation is higher than the previous one – this is due to changes in our diet.
As for completeness, if it is caused by errors in the diet, this feature is not inherited. Metabolic disorders can be passed on from generation to generation.
The cells of our body divide all the time. And each time the hereditary material enclosed in DNA is copied during division.
At the same time, errors (mutations) often occur: a DNA fragment is lost or one of its sections is incorrectly copied. Cells of the immune system destroy “breakdowns”. If this does not happen, during the next division, mutant cells transmit incorrect information to their daughter cells, which causes genetic diseases.
Fortunately, nature has created two copies of the genes. When only one gene mutates, nothing terrible will happen.
But when the “breakdown” falls on the dominant gene, the genetic disease is inherited by children.
If the X chromosome mutates, the woman will be the carrier of the genetic disease. She has a 50% chance of transmitting her “broken” chromosome to her son, since women have 2 copies of the X chromosome (XX), for men, she is the only one (XY), and they receive it from her mother.
But science is developing, and now, thanks to prenatal diagnosis, it is possible to determine whether the child will receive a defective gene – in other words, whether the boy becomes ill and the girl becomes the carrier.
More and more future parents, planning to increase the family, undergo a full medical examination. You should start with a visit to a genetics doctor: he will compose a pedigree and check the karyotype of both parents, that is, make detailed maps of their chromosomes and determine if the family is at risk. With the help of prenatal diagnosis, most of the congenital and hereditary problems in a child can be eliminated during pregnancy.
It is primarily about such chromosomal abnormalities as: Down syndrome (the presence of an extra 21st chromosome), Edwards syndrome (an extra X chromosome), Turner syndrome (not enough X chromosome). It is also important to make sure that the child is not threatened with gene diseases: hemophilia, phenylketonuria, Duchenne muscular dystrophy, cystic fibrosis and others.