What is inheritance?

We explain what is inheritance, types of inheritance that exist and why it is important. Also, what are genotype and phenotype.

1. What is inheritance?

In biology and genetics , inheritance 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. This transmission is due to genes , minimum units of biological information contained in chromosomes and expressed molecularly in the DNA matrix.

Inheritance encompasses a process in paradoxical appearance, of constancy and variation : certain general characteristics of the species remain intact over the generations, while a wide variation occurs among 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 transmitted to offspring and others not. In these alterations, typical of the random combinatorial of genetic processes, there may be ailments, diseases, metabolic patterns and even, perhaps, behavioral traits.

2. Types of inheritance

Thanks to genetic studies of over a hundred years of research , today we know that inheritance can occur in four different ways , according to the way in which genes are arranged inside the chromosomes. These forms are:

• Dominant.  Those inherited traits that show a preference for manifesting 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 sort of combinatorial, without either dominating and the other being recessive.
• Intermediate. Also called partial dominance, it occurs when the dominant gene fails to manifest itself at all and does so halfway, resulting in an intermediate situation, of a tie between the genes, manifested halfway.

3. Importance of inheritance

Genetic inheritance is vital to the existence and continuity of life as we know it . In fact, arguably it is a biological trait that gives purpose to life : the spread of the genome of the species and its gradual adaptation to the environment, ensure that all the species survive, although individuals perish.

Inheritance also allows evolution  to the extent that the acquired and successful advantages can be transmitted to the offspring, which in radical cases can mean the creation of a completely new (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 to the new generations the genetic memory of the species. Without inheritance, reproduction does not make much sense .

4. Genotype and phenotype

The genome is the genetic framework of the species , part of what remains unchanged throughout the generations (unless, as it happens 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 possess the entire genotype of the organism in their DNA, except for sexual cells or gametes, which have half the genetic load, since their purpose is to mix that genotype medium with the other genotype half of the opposite gamete during fertilization (ovules and sperm).

This genotype, on the other hand, materializes in a series of physical and perceptible characteristics that form the individual phenotype . 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 changes caused by their environment.

5. 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, the color of the eyes or hair) are contained in our genome because we receive them from our parents, through the burden 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 Industrial Revolution England , when factories and smog began to flood the airs and tree trunks. These pale-colored butterflies stood out on the walls obscured by soot and were therefore easier prey for predators. Such an environmental pressure caused a change in the pigmentation of the butterflies, which thereafter changed their colors to an opaque gray or brown. Being less detectable, the butterflies proliferated and reproduced, transmitting to their offspring the genes of the dark color, which in turn guaranteed them a greater probability of subsistence.