The appearance of an organism is called its phenotype. In this context, the phenotype is shaped both genetically and by the environment. Natural phenotypic changes in an organism are usually caused by environmental factors.
What is phenotypic change?
Natural phenotypic changes to an organism are usually caused by environmental factors. Phenotypic changes can occur in an individual organism or within a population of organisms. Each individual organism is initially born with a particular phenotype, which is determined by its genetic makeup. However, when considering genetic makeup alone, we speak of genotype. In the course of life, this genotype is constantly changed by environmental influences, which causes the phenotypic appearance. It is also always in a state of change. In this case we speak of modification. However, within a population of living organisms, phenotypic changes of organisms can also occur due to genetic changes. These are processes of epigenetics and evolution. Phenotype includes all external appearances such as size, hair color, skin color or eye color. Internal (physiological) characteristics concern the functioning of the internal organs, the structure of the musculature and also the occurrence of certain diseases. In contrast to the genotype, behavioral traits in particular also belong to the phenotype. Some characteristics are genetically determined and cannot be changed (e.g. eye color). Other traits are more variable and are subject to modification in the course of life. These include weight, for example.
Function and task
Each individual organism undergoes several phenotypic changes during physical development. Already during human development, for example, changes occur that are manifested in their size or sexual maturity. However, these changes are genetically pre-programmed. They are caused, among other things, by internal hormonal changes (e.g. during puberty). How these changes take place and which phenotypic changes occur, however, in turn depends on external influences. For example, growth is influenced by nutritional status as well as other factors. The better the nutrition, the taller the individual can become. Body weight is also highly variable. In addition, behavior depends mainly on the educational influence of parents and school, as well as social factors. Each trait is genetically predisposed, but whether this predisposition is retrieved depends on environmental influences. Thus, there are predispositions for higher body weight, for height, but also for certain behavioral traits. Many physical traits, however, also develop differently in different environments. For example, identical twins with the same genotype can develop completely differently in different environments. There can also be deviations in appearance. Later life often determines physical fitness and even health development. This phenological variability is often very useful. It enables a flexible reaction to different environmental influences. For example, humans can gain experience and incorporate it into their behavior. By gradually changing the way he responds to environmental stimuli, the opportunity to react flexibly is formed for him. Without this flexibility, human society could not have developed in this form. The degree to which the phenotype can be influenced by environmental stimuli is also called the reaction norm. This reaction norm of individual traits is in turn genetically determined. For example, the variability of weight was vital in earlier human populations. For example, periods of hunger could be bridged by first creating body reserves. In societies with sufficient food supply, however, this possibility of variation has lost its necessity. In phenotypic changes, the genotype of the individual organism is not altered. However, according to current findings, epigenetic processes play a role. As part of these processes, certain genes are preferentially activated and others inactivated. Epigenetics sets the boundaries within which an organism’s phenotypic changes can occur.It should also be mentioned that within a population of organisms, due to changes in the environment, genetic changes (mutations) are also preferred over several generations, which are better adapted to the new environment. In this case, phenotypic changes within the population also have real genetic changes as their basis.
Diseases and disorders
Phenotypic changes are not always desirable. This is particularly evident in the example of body weight. Body weight represents a highly variable body characteristic. Genetically, there is a predisposition to obesity, but with a normal-calorie diet and adequate physical activity, weight will not increase. However, there are also people who cannot gain weight because of metabolic adaptation to energy intake. As it is known, overweight is a risk to health. Whether it comes to the outbreak of certain diseases is then still dependent on the lifestyle and other genetically determined predispositions. For example, not every obese person develops diabetes mellitus. Furthermore, hereditary factors for lipometabolic disorders may exist, but these only take effect with a certain lifestyle. Cardiovascular diseases are also dependent on lifestyle, body weight and genetic predispositions. In contrast, a very healthy lifestyle can prevent the onset of a genetically predisposed disease. Thus, the appropriate environmental conditions often influence the length of life and quality of life, even though a particular genetic constellation may not prove favorable. Even people with obviously genetic diseases can sometimes develop very well with good support and therapy. In the case of the genetically determined metabolic disorder phenylketonuria, for example, a special diet only has to be followed during childhood to prevent the symptoms from occurring. Hormone-related predispositions can also lead to significant physical changes. For example, in women, increased testosterone production in the adrenal glands can result in a more masculine appearance. Conversely, men may develop secondary female sexual characteristics as a result of increased estrogen production. However, this is not a health or medical concern, but is merely a possible variation. The only disadvantages of this variation arise from the social interpretation that this is abnormal.
