We have long known that genes play a crucial role in the existence of all living things. But how exactly do they work? What are recessive and dominant traits, how are they transmitted? We learn about it further.
Information about the color of our hair, eyes, growth, susceptibility to disease lies in the chromosomes. In the nuclei of human germ cells (sperm and eggs) 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 chromosomes are composed of DNA molecules - deoxyribonucleic acid, which is a long compound of two chains of nucleotides. The chains are very long; therefore, they are twisted together in tight spirals, supported by hydrogen bonds.
The main component of the DNA is the gene. This is a small part of the molecule. It has a fixed location and a certain number of nucleotides that are in strict sequence. The order of the nucleotides is called the genetic code.
Chromosome carries a huge number of genes, which are distributed linearly on it, each in its place. In the process of the formation of a new organism, each chromosome of the maternal and paternal cells "sends" to merge its copy. So, the first maternal chromosome joins the paternal chromosome of the same order.
Genes located on the same stretch of chromosomes are called allelic. They are responsible for the same hereditary features, for example, hair color. Two identical genes cannot manifest simultaneously, therefore, for a particular individual, only one of the two alleles appears.
Often, genes are responsible for several signs at once. For example, red-haired skin is almost always light. There are dominant and recessive genes. If one trait suppresses the manifestation of another, it is a dominant trait.
Recessive and dominant traits
Predicting which genes will prevail in a particular case is not easy. Science is only developing methods that allow it. 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 totality of all the genes in the chromosomes, a kind of genetic potential of a particular person. Differently combined with each other, they represent a phenotype - a set of manifested external and internal features.
In nature, the dominant feature is dark curly hair, dark eye color. But even if both parents have strong traits, the weak, recessive genes of a grandmother or grandfather have a chance to manifest themselves in their grandchildren. Inheritance sometimes occurs from the most distant relatives.
What are the dominant signs?
To better understand what are the recessive and dominant signs of a person, let's turn to the table. Here, the obviously strong and weak features are simplified.
Some of the signs are rather ambiguous. The same can be either dominant or recessive, depending on which attribute is his “opponent”. As can be seen from the table, the blue eye gene will always be recessive, but the green one is recessive only in relation to the caramel color.
Types of domination
If it all comes down to the fact that strong genes suppress weak ones, where does diversity come from? After all, even eye colors are represented by a much larger palette than green, brown and blue. Why are we sometimes so different from each other? It is not only our ancestors and the genotype inherited from them.
Gene suppression can occur with different strengths. In addition to complete dominance, there is an incomplete. In this case, the dominant trait is not fully manifested, but also recessive. The result is something average. For example, in a family where one parent has curly hair and the other has straight, the child may have wavy.
There is also a codominance of genes when none of them manifests dominance. In this case, the offspring observed signs from both parents equally. Co-dominance is similar to incomplete dominance, however, in the latter case, the features of the parents are mixed. An example would be a pink flower, derived from a mixture of white and red. If these flowers were codominant, the flower would have turned out with white and red spots.
In humans, a bright example of codominance is the IV (AB) blood group. It can occur when the parents of group II and III, which are designated as AA or BB.