Heredity is responsible for making children resemble their relatives. Within the framework of complex processes, various characteristics are passed on to descendants via the chromosomes. In the process, two expressions for each trait always meet through the mother and father.
What is heredity?
Humans have 46 chromosomes. Chromosomes are carriers of DNA, on which all information for physical appearances is stored. Humans have 46 chromosomes. Chromosomes are carriers of DNA, on which all information for physical appearances is stored. For example, they decide which eye color will develop or what size the offspring will reach. There are 46 chromosomes in each cell of the body, excluding the germ cells, which divide during meiosis. The diploid set of chromosomes comes in equal parts from mother and father. Chromosomes are the starting point of heredity. There are various rules and characteristics according to which traits are inherited. Decisive for the great genetic diversity in a population is above all the recombination of alleles. Alleles are individual components of chromosomes. In this way, evolution can take place simultaneously in the long term, as soon as adaptation to new living conditions becomes necessary.
Function and task
The conspicuousness that children often look very much like their parents has been known for a long time. How such a phenomenon comes about, however, was only gradually deciphered in 1865 by Gregor Johann Mendel. He conducted experiments with peas and was thus able to name processes according to which characteristics of plants are passed on. However, these regularities cannot be transferred one-to-one to humans. Instead, it is a much more complex process. In total, there are about 25,000 genes in the chromosomes of humans. These ultimately determine the appearance and the course of metabolic processes. The genetic variance is almost infinite. In total, there are about 64 trillion possible combinations, which ultimately ensure that although people are similar, they still differ from one another. In the end, heredity ensures that there are two blueprints (each from mother and father) for all characteristics in every cell. Which characteristic will prevail is decided at a very early stage. Thus it comes to the fact that certain characteristics are inherited dominantly, while others remain recessive. It is not possible to exert any influence on which trait will prevail. In this case, the parents carry recessive genes, which can develop into a dominant gene in the course of inheritance. For example, it is possible that mother and father have black and blond hair. As a rule, black hair is inherited dominantly. However, the mother can just as well carry a gene for blond hair, which did not assert itself in herself, but now possibly unites with the same gene of the father, whereby the offspring finally also receives blond hair. Due to the existing, but unexpressed, inherited genes, which are ultimately retrieved in the descendants, it is also possible for grandchildren to resemble their grandparents or more distant relatives. Ultimately, every person carries genes that have not been able to assert themselves in their own appearance. Inheritance of these characteristics is nevertheless possible. The most important task of heredity is thus the production of genetic diversity. This is also of great importance for evolution.
Diseases and disorders
In the context of heredity, diseases can occur. Various hereditary diseases exist that are passed on according to certain patterns. For example, albinism, cretinism and Peters-Plus syndrome are inherited autosomal recessively. The starting point here is again the chromosomes. In autosomal inheritance, the defective gene is located on one of the chromosomes that are not responsible for determining sex. However, for the disease to take hold and be transmitted to offspring, both parents must have the damaged gene. Only in this way is there a possibility of disease. However, it is not necessary for the parents to actively suffer from the disease. Instead, they can also be carriers, in that the trait has not become established in them, but it is nevertheless present in the genetic material.In autosomal dominant diseases, on the other hand, the presence of a defective gene is sufficient to trigger the disease. Thus, the child’s risk of contracting the disease is 50 percent. Diseases inherited in an autosomal-dominant manner include, for example, sickle cell anemia or Marfan syndrome. In addition to autosomal inheritances, there are also those that are transmitted via the gonosome. For example, genes that cause hemophilia or red-green blindness are located on the X chromosome. Women have two X chromosomes, men one X and one Y chromosome. In the case of X-linked inheritance, the sex of the parents and of the child is decisive. For example, if a man carries a defective gene on his X-gonosome, all his daughters will be carriers of the disease despite a healthy mother. This is based on the fact that the children receive one X chromosome from the father and one from the mother in order to develop their sex. If the woman also has the defective gene, all offspring will have the expression for a certain disease. If only the woman is affected, her sons get the disease, while her daughters are carriers. If carriers have children, they will be carriers, healthy, or diseased in equal numbers.
