We have known for a long time that genes play a vital role in the existence of all living things. But how exactly do they work? What are recessive and dominant symptoms, how are they transmitted? We will learn more about this.
Information about the color of our hair, eyes, growth, susceptibility to diseases lies in the chromosomes. In the nuclei of human germ cells (spermatozoa and ovules) they contain 23. Only one, the largest, is responsible for the sex of the person. The rest are called autosomes, they carry other hereditary traits.
The structure of chromosomes includes molecules of DNA - deoxyribonucleic acid, which is a long connection of two nucleotide chains. The chains are very long, so they are twisted together in dense spirals supported by hydrogen bonds.
The main constituent of DNA is the gene. This is a small portion of the molecule. It has a fixed place and a certain number of nucleotides, which are in strict sequence. The order of nucleotides is called a genetic code.
The chromosome carries in itself a huge number of genes, which are distributed linearly on it, each in its place. In the process of formation of a new organism, each chromosome of the maternal and paternal cells "sends" its copy to the fusion. Thus, the first maternal chromosome joins the paternal chromosome of the same order.
Genes located on the same segment of chromosomes are called allelic. They are responsible for the same hereditary characteristics, for example, for the color of the hair. Two identical genes can not simultaneously manifest themselves, therefore, in a particular individual the gene of only one of the two alleles is manifested.
Often, genes are responsible for several signs. For example, red-haired skin is almost always light. There are dominant and recessive genes. If one sign suppresses the manifestation of another, it is a dominant feature.
Recessive and dominant signs
To guess which genes will prevail in a particular case is not easy. Science only develops methods that will allow it to be done. Despite the existence of strong and weak genes, the dominant trait does not always win.
The genetic mechanism works much harder. Blue-eyed children, for example, may appear in brown-eyed parents. It's all about the genotype-the aggregate of all genes in chromosomes, the peculiar genetic potential of a particular person. Differently combining among themselves, they represent a phenotype - a set of manifested external and internal traits.
In nature, the dominant feature is a dark curly hair, a dark eye color. But even if both parents have strong features, the weak, recessive genes of grandparents have a chance to manifest themselves in grandchildren. Inheritance sometimes comes from the most distant relatives.
What are the dominant signs?
To better understand what are the recessive and dominant signs of a person, let us turn to the table. Here, simplistically, known are strong and weak features.
Some of the signs are rather ambiguous. The same can be either predominant or recessive, depending on which attribute is its "opponent". As can be seen from the table, the gene of the blue eyes will always be recessive, but the green recessive only in relation to the carem color.
Types of dominance
If it all boils down to the fact that strong genes suppress the weak, where does the diversity come from? Even the colors of the eyes are represented by a much larger palette than green, brown and blue. Why do we sometimes differ so much from each other? The point here is not only in our ancestors and inherited from them genotype.
Suppression of genes can occur with different strengths. In addition to complete domination, there is incomplete. In this case, the dominant sign does not manifest itself to the full, but also recessive. In the end, something turns out average. For example, in a family where one parent has curly hair and the other has straight hair, the child may have wavy hair.
There is also the codonage of genes, when none of them shows dominance. In this case, the offspring exhibit signs from both parents in equal measure. Co-domination is similar to incomplete dominance, however, in the latter case, the traits of parents are mixed. An example is a pink flower obtained from mixing white and red. If these flowers had a codomination, the flower would have turned out with white and red spots.
In humans, a vivid example of codomination is the IV (AB) blood group. It can arise when the parents II and III group, which are designated as AA or BB.