Monogenic and polygenic features

Genetics explores how organisms transmit biological information and how it is being used in life. Biological information is located in the DNA molecule and it is the basis of biological function. Biological functions are carried out primarily by protein molecules that are specified through record in the DNA molecule or its "units of inheritance" - genes.

Difference among individuals is determined by two main groups of factors: internal, which are written in our genes and external factors that make all the environmental factors, lifestyle, living conditions, habits and social factors.
Gene controls one or more characteristics of organism and is presented by two alternative forms which are called alleles, located in a certain place of homologous pairs of chromosomes.

For every feature organism inherits two alleles (one from each parent).
Each of the morphological features is visible by eye (appearance) or function in the body makes so called phenotype - the result of interaction of genotype and environmental factors. A number of features are under the control of a single gene. Such features are inherited by the famous Mendel law of inheritance and they are called monogenic features. Second part is controlled by multiple genes and is called polygenic feature.

When we talk about genes and individual genetic polymorphisms people often wrongly think that always one gene or polymorphism determines the phenotype, or feature. However, there are more processes that regulate each feature or protein expression. A large part of this process is not yet known. While their biological basis is not finally defined, the relationship between genotype and phenotype also may not be clear and obvious, and it is difficult to determine in advance precisely how much the relationship between genes and environment will affect the appearance, behavior or appearance of the disease.

For example, eye color is a polygenic feature. It is determined by the amount of pigment in the eye, or the amount of melanin in the iris, which are defined by a large number of genes. The actual number of genes that determines or affects the eye color is not known. Examples of polygenic features are also hair color, height, weight, intelligence, etc. Personality and behavior can also be included in this group. In addition to the fact that these characteristics are polygenic, previously mentioned external factors also affect them. We can say that these features have multifactor properties. Therefore, it is difficult to say how much we will resemble our parents because all the genes are not yet defined and also the polymorphisms that define them, as it is difficult to know in advance to which environmental, social factors we will be exposed or which habits we will adopt and what will be the interaction with the record in our genes.

If we talk about diseases, there are also polygenetic and multifactor diseases or conditions - such as cardiovascular diseases, diabetes or obesity and monogenetic diseases - for example, hemophilia or thalassemia.

Genetic analysis has enabled the understanding of molecular basis of some diseases and caused a major shift in the diagnosis and clinical approach, not only to primarily monogenic but also to polygenic diseases, as well. Numerous genes responsible for polygenic disease manifestation are defined which allowed the individualization of diagnosis, prevention, treatment and therapy.

However, it is important to emphasize that genetic testing is not universal or diagnostic method and that all the facts are not yet known so we must always think of the environmental impact, lifestyle and habits.

Advances in molecular and medical sciences and technology, individualization in diagnosis and treatment will be even bigger, more accurate and more broadly applicable both in monogenetic and polygenetic diseases and conditions.
Along with these processes ethical issues must not be neglected such as the exposure of individuals to unnecessary anxiety or false security, or possibilities for misuse of information. Any information relating to genetic inheritance or risk inheritance has to have a purpose in possible and justified intervention in terms of prevention or treatment. It is always important to assess the benefit brought by information in relation to "damages" and the possibility of effective intervention in terms of preventive measures or treatment.
 
 
Ana Puljak, MD