‘Constitutions’, ‘constitutional symptoms’ and ‘consitutional drugs’ are concepts which play a very important role in homeopathic theory and practice. Concepts such as ‘genetic constitution’ and ‘miasmatic constitution’ are frequently heard in homeopathic discussions. There have been a lot of attempts to explain constitution in terms of 'miasms', genetics, embryology and many other concepts.

I am trying to evolve a scientifically viable understanding of our concept of 'constitution'. I think it would be more logical and scientific if we understand 'constitution' in terms of ‘phenotypes’ of individuals. To understand and explain ‘constitutions’ in scientific terms, we have to understand the concepts of ‘genotypes’ and ‘phenotypes’ in modern genetics.

According to modern genetics, the ‘genotype’ is the ‘genetic substance or ‘DNA’ inherited by the organism from its previous generation. It is called the ‘genetic blue print’.

The ‘genotype’ contained the organism gives rise to individual ‘phenotypes through ‘gene expressions’. The ‘genetic code’ stored in DNA is interpreted by ‘gene expression’, and the properties of these expressions five rise to the ‘phenotype’ of the organism.

A ‘phenotype’ is the observable characteristics or traits of an organism, such as morphology, development, biological and physiological properties, behavior, and products of behavior. ‘Phenotype’ is the result of ‘gene expressions’, which is decided by the interaction between genetic blue print and environmental factors.

‘Genotype’ of an organism is the inherited instructions it carries within its genetic code. Organisms with same ‘genotype’ do not appear or act the same way, because its ‘phenotype’ is decided by the interaction with environmental and developmental conditions. Similarly, not all organisms that look alike necessarily have the same genotype.

This understanding of ‘genotype-phenotype distinction’, proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism's heredity and what that heredity produces, is very important in providing a scientific explanation for the homeopathic concept of ‘constitutions’.

Despite its seemingly straightforward definition, the concept of the phenotype has some hidden subtleties. Some would argue that anything dependent on the genotype is a phenotype, including molecules such as RNA and proteins. Most of the molecules and structures coded by the genetic material are not visible in the appearance of an organism, yet they are observable and are thus part of the phenotype. Human blood groups are an example. Others would say that this goes beyond the original intentions of the concept with its focus on the (living) organism in itself, meaning that the lowest level of biological organization compatible with the phenotype concept is at the cellular level. Either way, the term phenotype includes traits or characteristics that can be made visible by some technical procedure. Another extension adds behavior to the phenotype since behaviors are also observable characteristics. Indeed there is research into the clinical relevance of behavioral phenotypes as they pertain to a range of syndromes.

Phenotypic variation (due to underlying heritable genetic variation) is a fundamental prerequisite for evolution by natural selection. It is the living organism as a whole that contributes (or not) to the next generation, so natural selection affects the genetic structure of a population indirectly via the contribution of phenotypes. Without phenotypic variation, there would be no evolution by natural selection.

The relationship between ‘genotype’ and ‘phenotype’ has often been conceptualized by the following relationship: “genotype (G) + environment (E) + genotype & environment interactions (GE) → phenotype (P)”

‘Genotypes’ often have much flexibility in the modification and expression of phenotypes; in many organisms these phenotypes are very different under varying environmental conditions. The concept of phenotype can be extended to variations below the level of the gene that affect an organism's fitness. For example, silent mutations that do not change the corresponding amino acid sequence of a gene may change the frequency of guanine-cytosine base pairs (GC content). These base pairs have a higher thermal stability than adenine-thymine, a property that might convey, among organisms living in high-temperature environments, a selective advantage on variants enriched in GC content.

A phenotype is the ensemble of observable characteristics displayed by an organism. The idea of the phenotype expresses all the effects a gene has on the outside world that may influence its chances of being replicated. These can be effects on the organism in which the gene resides, the environment, or other organisms.

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as ribosomal RNA (rRNA), transfer RNA (tRNA) or Small nuclear RNA (snRNA) genes, the product is a functional RNA. The process of gene expression is used by all known life to generate the macromolecular machinery for life.

Several steps in the gene expression process may be modulated, including the transcription, RNA splicing, translation, and post-translational modification of a protein. Gene regulation gives the cell control over structure and function, and is the basis for cellular differentiation, morphogenesis and the versatility and adaptability of any organism. Gene regulation may also serve as a substrate for evolutionary change, since control of the timing, location, and amount of gene expression can have a profound effect on the functions (actions) of the gene in a cell or in a multicellular organism.

Factors, such as such as miasmatic, environmental, nutritional, occupational, infectious, emotional, ontogenic, metabolic and xenobiotic influence the process of ‘gene regulation’ at various stages of ‘gene expression’, through which the particular ‘phenotype’ or ‘constitution’ of the individual organism is determined. As such, ‘constitution’ of an individual is the ‘phenotype’ determined by the ‘protein constitution’ developing through ‘genetic expression’’Constitution’ is expressed in the form of totality of general physical symptoms, morphology, mental symptoms and behavioral peculiarities.

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