We explain what inheritance is, the types of inheritance that exist and why it is important. Also, what are the genotype and phenotype.
What is inheritance?
In biology and genetics, heredity is understood as the sum of the processes by which the physical, biochemical or morphological characteristics of living beings are transmitted from parents to their descendants. Said transmission it is given thanks to the genes, minimal units of biological information contained in chromosomes and expressed molecularly in the DNA matrix.
The inheritance encompasses a seemingly paradoxical process of constancy and variation: certain general characteristics of the species remain intact over the generations, while there is a wide variation between individuals of the same species. This is possible because each of them has the same genetic framework (genome) determined by the species, but expressed in an absolutely unique configuration of genes, which only identical twins share.
The genetic content of individuals is replicated during cell division (specifically during nucleus replication) and is susceptible to mutations or alterations, some of which can be passed on to offspring and some of which cannot. In these alterations, typical of the random combinatorial of genetic processes, there may be ailments, diseases, metabolic patterns and even, perhaps, behavioral traits.
Types of inheritance
Thanks to genetic studies of more than one hundred years of research, today we know that heredity can occur in four different ways, according to the way the genes are arranged inside the chromosomes. These forms are:
- Dominant. Those inherited traits that show a preference for manifesting themselves and that, therefore, are present in the phenotype of the individual.
- Recessive Those inherited traits that are present in the genome but not manifest. They can manifest only when they are not in the presence of a dominant gene.
- Codominant. In certain cases, both characters can be expressed at the same time in a kind of combinatorial, with neither dominating and the other being recessive.
- Intermediate. Also called partial dominance, it occurs when the dominant gene fails to manifest at all and does so half, which results in an intermediate situation, of a tie between the genes, half manifest.
Importance of inheritance
Genetic inheritance is vital for the existence and continuity of life as we know it. In fact, it could be said that it is a biological trait that gives life a purpose: the propagation of the genome of the species and its gradual adaptation to the environment, guarantee that the entire species survives, even if the individuals perish.
The Heritage also allows evolution insofar as the acquired and successful advantages can be passed on to the offspring, which in radical cases can mean the creation of a completely new one (speciation).
Without inheritance, life would be prevented from growing in complexity and diversification, and species could hardly aspire to repeat themselves in a vacuum, without being able to transmit the genetic memory of the species to new generations. Without inheritance, reproduction does not make much sense.
Genotype and phenotype
The genome is the genetic framework of the species, part of what remains unchanged throughout the generations (unless, as in evolution, there is such a radical and successful variation that it gives rise to the appearance of a new species). Each individual has a unique and unrepeatable expression of said genome, that is, a total genetic information of their organism, which we will call genotype.
All nucleated cells of the human body have the entire genotype of the organism in their DNA, except sex cells or gametes, which have half the genetic load, since their purpose is to mix that half genotype with the other half genotype of the opposite gamete. during fertilization (eggs and sperm).
This genotype, on the other hand, is materialized in a series of physical and perceptible characteristics, which form the phenotype individual. However, although the genotype is the genetic information that governs the phenotype in principle, the latter will also be determined by the environment in which the individual develops, so that:
Genotype + Environment = Phenotype.
In this way, some specific conditions of each individual will be attributable to their genotype, while others will be the product of the dynamics of change caused by their environment.
Examples of inheritance
If we want to see examples of inheritance, it will be enough to go to a genealogical album or to our own family. Those common traits with them (physical resemblance, common diseases or weaknesses, eye or hair color) are contained in our genome because we receive them from our parents, through the load of their DNA used to create ours. .
Another example of inheritance is evolution by natural selection.. A famous case is that of the birch butterflies of the England of the Industrial Revolution, when factories and smog began to flood the airs and the trunks of the trees. These pale-colored butterflies stood out on the soot-darkened walls and were therefore easier prey for predators. Such environmental pressure caused a change in the pigmentation of the butterflies, which thereafter changed their colors to a dull gray or brown. Being less detectable, the butterflies proliferated and reproduced, transmitting the genes of the dark color to their offspring, which in turn guaranteed them a greater probability of survival.