Two important concepts for the development of genetics at the beginning of the 20th century were those of phenotype and genotype , created by the Danish researcher Wilhelm L. Johannsen (1857-1912).
The term “phenotype” (from the Greek pheno , evident, bright, and typos , characteristic) is used to designate the characteristics presented by an individual, be they morphological, physiological and behavioral. Also part of the phenotype are microscopic and biochemical characteristics that require special tests for their identification.
Among the visible phenotypic characteristics, we can mention the color of a flower, the color of a person’s eyes, the texture of the hair, the color of an animal’s hair, etc. Already the blood type and amino acid sequence of a protein are phenotypic characteristics revealed only by special tests.
The phenotype of an individual undergoes transformations over time. For example, as we age our bodies change. Environmental factors can also alter the phenotype: if we are exposed to sunlight, our skin will be darkened.
The term “genotype” (from the Greek genos , to originate, to come, and typos , characteristic) refers to the genetic constitution of the individual , that is, to the genes that he possesses. We are referring to the genotype when we say, for example, that a pea plant is dominant homozygous (VV) or heterozygous (Vv) in relation to the color of the seed.
Phenotype: genotype and environment in interaction
The phenotype results from the interaction of the genotype with the environment. Consider, for example, two people who have the same types of alleles for skin pigmentation; if one of them takes sun more often than the other, their skin tones, phenotype, are different.
An interesting example of interaction between genotype and environment in phenotype production is the reaction of Himalayan rabbits to temperature. At low temperatures, the hairs grow black and, at high temperatures, they grow white. The normal coat of these rabbits is white, except at the extremities of the body (snout, ear, tail and legs), which, because they lose more heat and have a lower temperature, develop black coat.
Determining the genotype
While the phenotype of an individual can be directly observed, even through instrumentation, the genotype has to be inferred by observing the phenotype, by analyzing its parents, children and other relatives, or by sequencing the individual’s genome , that is, reading what is in the genes. The technique of sequencing is not widely used because of its high cost and the need for specialized equipment. Therefore, observation of the phenotype and analysis of relatives is still the most used feature to know the genotype.
When an individual presents the phenotype conditioned by the recessive allele, it is concluded that he is homozygous for the allele in question. For example, a green pea seed is always homozygous vv. An individual who presents the phenotype conditioned by the dominant allele may be homozygous or heterozygous. A yellow pea seed, for example, may have a VV or Vv genotype. In this case, the genotype of the individual can only be determined by the analysis of his parents and their descendants.
If the individual with the dominant phenotype is the child of a father with a recessive phenotype, he will certainly be a heterozygote, since he inherited a recessive allele from the father. However, if both parents have dominant phenotype, nothing can be said. It will be necessary to analyze the offspring of the study subject: if any child exhibits the recessive phenotype, this indicates that he is a heterozygote.
Difference between genotype and phenotype
the phenotype only includes the expressed genes while the genotype includes all genetic information , including the unexpressed gene .
Consider the gene that determines the color of a person’s hair. As humans we are diploids, each cell has 2 alleles of each gene. A person may have the allele for brown hair and the allele for blond hair. If this person has brown hair, his phenotype includes the chestnut allele, which is the one that has been expressed, while the genotype includes the two alleles.
In addition, the environment influences the phenotype but not the genotype , which is determined only by genetic inheritance. To determine the genotype of an individual, one must study its genetic map and identify the alleles of each of its genes. In order to determine its phenotype, it is only necessary to observe it.
It is very frequent that the phenotype is associated with morphological features but in fact is the set of any observable characteristic . This includes morphological but also behavioral, biochemical, histological, etc. characteristics.
The set of phenotypic variability is known as polyphasia or polyphenism.
Heritage and environment
The genotype is determined by the genetic inheritance that the individual receives from his parents and this implies that he remains constant throughout his life. It only varies among different individuals due to mechanisms of genetic variability such as recombination that occurs during meiosis .
However, the environmental factor of the phenotype causes it to vary during the life of the individual as a function of external conditions and is not necessarily a characteristic transmitted from progenitors to offspring, since it may be due to the expression of a gene, to factors or a combination of both.
For example, the pink plumage of flamingos ( Phoenicopterus ) is a phenotypic trait that is due to environmental factors. Flamingos have white feathers and are substances ingested through the diet responsible for the color pink.
The environment has a great influence on the pink phenotype of flamingos
The level of influence of environmental factors on the phenotype is known as phenotypic plasticity . The greater the influence of the environment, the greater the phenotypic plasticity.