Phenotype: Definition, Examples, Relationship to Genotype, Genotypic Variations, Types and Inheritance

They are all the observable characteristics of an organism that result from the interaction of its genotype (total genetic inheritance) with the environment.

Examples of observable characteristics include behavior, biochemical properties , color, shape, and size.

On the other hand, the genotype of an individual is what we call the information that helps create that phenotype. There may be one gene responsible, or more than one.

And genes do not always show all their characteristics, sometimes the environment affects the phenotype.

The phenotype can constantly change throughout an individual’s life due to environmental changes and the physiological and morphological changes associated with aging.

Different environments can influence the development of inherited traits (such as size, for example, which is affected by the available food supply) and alter expression by similar genotypes (for example, twins growing in different families).

In nature, the influence of the environment forms the basis of natural selection, which initially works in individuals, favoring the survival of those organisms with phenotypes more suitable for their current environment.

The survival advantage conferred on individuals exhibiting such phenotypes enables those individuals to reproduce with relatively high success rates and thus pass on successful genotypes to subsequent generations.

The interaction between genotype and phenotype is remarkably complex, however.

For example, all the inherited possibilities in the genotype are not expressed in the phenotype, because some are the result of latent, recessive or inhibited genes.

One of the first to distinguish between elements passed from one generation to the next (the “germ” plasma) and the organisms that developed from these elements (the “soma”) was the late German biologist August Weismann. 19th century.

Germplasm was later identified with DNA, which carries the information for protein synthesis and their organization in a living body: the soma.

The modern understanding of the phenotype, however, is derived largely from the work of the Danish botanist and geneticist, Wilhelm Ludvig Johannsen, who in the early 20th century introduced the term phenotype to describe the observable and measurable phenomena of organisms.

Johannsen also introduced the term genotype, referring to the hereditary units of organisms.

Examples of phenotypes

Appearance-related traits are sometimes the easiest to observe.

When Gregory Mendel was doing his famous experiments with pea plants, he observed the appearance of the plants: the peas could be green or yellow, smooth or wrinkled.

Plants can also be regular or dwarf in height.

Humans also have physical appearance phenotypes such as height and eye color, which are phenotypes controlled by genes.

The behavior can also be a phenotype. Collies were bred to herd sheep, so even if they have never seen a sheep in their life, they will display herding behaviors.

Chemical reactions in the human body are called metabolism.

One phenotype that is related to metabolism is the condition known as lactose intolerance.

If the individual is lactose intolerant, they do not have the lactase enzyme, so they cannot digest lactose and will present specific symptoms when they consume dairy products.

Relationship between genotype and phenotype


This is the “external physical manifestation” of an organism.

These are the physical parts, the sum of the atoms, molecules, macromolecules , cells, structures, metabolism, energy use, tissues, organs, reflexes and behaviors; anything that is part of the structure, function, or observable behavior of a living organism.


This is the “internally encoded hereditary information” transmitted by all living organisms.

This stored information is used as a “blueprint” or set of instructions for building and maintaining a living creature.

These instructions are found in almost all cells (in the ‘internal’ part), they are written in a coded language (the genetic code), they are copied at the time of cell division or reproduction, and they are transmitted from one generation to another ( heritable).

These instructions are closely related to all aspects of the life of a cell or an organism.

They control everything from the formation of protein macromolecules, to the regulation of metabolism and synthesis.

The “internally encoded hereditary information,” or genotype, carried by all living organisms, contains the instructions that are used and interpreted by the cellular machinery of cells to produce the “external physical manifestation” or phenotype of the organism.

Therefore, all the physical parts, the molecules, macromolecules, cells and other structures, are built and maintained by the cells following the instructions given by the genotype.

As these physical structures begin to act and interact with each other, they can produce larger and more complex phenomena, such as metabolism, energy use, tissues, organs, reflexes, and behaviors; anything that is part of the structure, function, or observable behavior of a living organism.

Genotypic variations

In biology, any difference between cells, individual organisms or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of genetic potentials (phenotypic variation).

Variation can be shown in physical appearance, metabolism, fertility, mode of reproduction, behavior, learning and mental ability, and other obvious or measurable characteristics.

Genotypic variations are caused by differences in the number or structure of chromosomes or by differences in the genes carried by chromosomes.

Eye color, body shape, and disease resistance are genotypic variations.

People with multiple sets of chromosomes are called polyploids, many common plants have two or more times the normal number of chromosomes, and new species can emerge from this type of variation.

A variation cannot be identified as genotypic by observation of the organism, reproduction experiments must be carried out under controlled environmental conditions to determine whether the alteration is heritable or not.

Phenotypes are traits or characteristics of an organism that we can observe, such as size, color, shape, capacities, behaviors, etc. Not all phenotypes can actually be seen.

Blood type is a phenotype that can only be observed using laboratory techniques.

The phenotype can be determined by genes, environmental factors, or a combination of both.

Phenotypic variation, then, is the variability in phenotypes that exists in a population. For example, people have height, weight, and body shape that are phenotypes that vary.

Hair, eye color, and the ability to move the tongue are also variable phenotypes. All organisms can have phenotypic variation.

In plants, flower color and leaf shape are examples of variable phenotypes.

In bacteria, antibiotic resistance is a variable phenotype: some bacteria are resistant and survive antibiotic treatment, while others are susceptible and die when antibiotics are administered.

Types of phenotypic variations

When a characteristic or phenotype normally exists in a range or gradient, it varies continuously, as shades of gray rather than black and white.

It’s easy to think of examples of continuously varying phenotypes, such as height and skin color. Between the smallest person in the world and the tallest person in the world, any height is possible.

If a frequency graph were made of the range of heights or skin colors in a group of people, it would look like a bell curve, with intermediate phenotypes being the most common.

This is one way to recognize when variation is continuous. However, some phenotypes can vary discontinuously.

These phenotypes exist only at discrete intervals, as “black and white” differences.

For example, you may have an A, B, AB, or O blood type, but there is no intermediate blood type.

Causes of phenotypic variation

Expression of phenotypes can be caused by genes, environmental factors, or both.

When we refer to environmental factors, we are not necessarily talking about climate: environmental factors are agents in an organism’s environment or lifestyle that can influence it in various ways.

Thus the body weight of an individual can be influenced by genes, but it can also be affected by diet. This is a case, where diet is an environmental factor.

Variations caused by the environment can be the result of one factor or the combined effects of several factors, such as climate, food supply, and the actions of other organisms.

Phenotypic variations also include stages in the life cycle of an organism and seasonal variations.

These variations do not imply any hereditary alteration and, in general, are not transmitted to future generations; consequently, they are not significant in the evolution process.

Variations are classified as continuous or quantitative (uniform classification between two extremes, with most individuals in the center, such as height in human populations); or as discontinuous or qualitative (composed of well-defined classes, such as blood groups in man).

A discontinuous variation with several classes, none of which is very small, is known as a polymorphic variation.

The separation of most higher organisms into males and females and the appearance of various forms of a butterfly of the same species, each colored to blend in with different vegetation, are examples of polymorphic variation.


Heredity is the sum of all the biological processes by which particular characteristics are transmitted from parents to their descendants.

The concept of inheritance encompasses two seemingly paradoxical observations about organisms: the constancy of a species from generation to generation and the variation between individuals within a species.

Consistency and variation are actually two sides of the same coin, as is clear from the study of genetics.

Both aspects of heredity can be explained by genes, the functional units of hereditary material found within all living cells.

Each member of a species has a set of genes specific to that species.

It is this set of genes that provides the constancy of the species.

Among individuals within a species, however, variations can occur in the form each gene takes, providing the genetic basis for the fact that no two individuals (except identical twins) have exactly the same traits.

The set of genes that an offspring inherits from both parents, a combination of each parent’s genetic material, is called a genotype.

The genotype is contrasted with the phenotype, which is the external appearance of the organism and the development result of its genes.

Although the genotype determines the wide limits of the characteristics that an organism can develop, the characteristics that actually develop depend on the complex interactions between genes and their environment.

The genotype remains constant throughout the life of an organism; however, because the body’s internal and external environments change continuously, so does its phenotype.

When conducting genetic studies, it is crucial to discover the degree to which the observable trait is attributable to the pattern of genes in cells and to what extent it arises from environmental influence.

Because genes are an integral part of explaining hereditary observations, genetics can also be defined as the study of genes.

Discoveries about the nature of genes have shown that genes are determinative in all aspects of an organism.

For this reason, most areas of biological research now have a genetic component, and the study of genetics holds a position of central importance in biology.

Genetic research has also shown that virtually all organisms on this planet have similar genetic systems, with genes that are based on the same chemical principle and that function according to similar mechanisms.

Although species differ in the sets of genes they contain, many similar genes are found in a wide range of species.