Oct 17, 2019 in Science

Behavior and Genetics

Many people, undoubtedly, wonder within their lives why humans differ so widely in the thirst for risks, in the exposure to mental illness, and in the productivity in intelligence tests. Partly, the disclosure of secrets that are questioned above comes from scientists who are occupied in the field of genetics. Thus, geneticists indicate that the variation in traits in people, in part, depends on the genetic structure of an organism. Under genetics, one should understand the study, which is aimed to interpret the term ‘gene’ and explore how genes function. Genes can be considered as units inside a cell that are destined to control the manifestations of inherited features in living organisms from their ancestors. A typical example of genes’ involvement in heredity can be children that usually resemble their parents. The phenomenon occurs due to the genes passing from the ancestors to posterity. Moreover, the resemblance may be seen not only in appearance, but also in manners and behaviors. Such manifestations, respectively, belong to the field of study known as behavioral genetics. The explanation of its practical application in the science can be expressed in such a way: if the mankind wants to understand how people stay healthy or become ill, it is obliged to understand behavior and genetics and their correlation, as well. In other words, behavioral genetics focuses on studying how the inherited factors influence the people’s actions and what kinds of genes cause different models of behavior. The expectations of what behavioral genetics can do are great, but the scientists realize that a simple answer to such a complex question is unlikely to be found. The deeper delving into the genetics of complex behaviors, results in the finding that such behaviors are affected by numerous interacting genes, each elucidating only a small segment of the overall variation. The challenges similar to the mentioned one make behavioral genetics research even more interesting and involving. The other reasons that can raise the reader’s interest in the discussed branch of science include its historical background investigation, tools and methods for searching genes, and prospects for gene therapy.

Before the further exploration the topic, it is worth to get the intelligible representation of the human genome, since exactly the latter results in the formation of posterity’s traits. The human genome is the term for all the genetic information contained in humans. It contains two sets of twenty-three chromosomes. A chemical substance, known as DNA (deoxyribonucleic acid) is the basic component of these chromosomes. In its turn, DNA consists of smaller units, which are linked and paired together to build a double-stranded spiral. The order of those units in DNA is called the genetic code, which is crucial at detecting the information applicable for maintaining and building an organism. Genetic coding, which occurs in cells, may specify the human behavior and the other traits as well. That coding proceeds in the nervous system, namely, in the spine, the brain, and nerves. The nervous system is responsible for spreading information chemically or electrically throughout the body. The field of science that studies the described operations is called behavioral genetics. It explores the genetic basis of intelligence and such personality characteristics as empathy, depression, predisposition to addiction, impulse control, and sexual orientation. Behavioral geneticists examine the contribution of genetic as well as environmental factors in the formation of human and animal behavior. They try to discover for what exposure the people's behavior is determined by the genetically inherited information and how much it is provoked by their learning choices, living conditions, or other circumstances from the world around them. This branch of science can be considered interdisciplinary, since it involves contributions from psychology, biology, epigenetics, ethology, and statistics.

 

The historical background of behavioral genetics deserves special attention of the reader. The circumstance that people act in different ways, especially if to speak about abnormal or antisocial types of behavior, has caught scientists’ attention long before our days. One cannot distinguish when the behavioral genetics came to be considered a separate scientific subject. Usually, it is accepted that the publication of “Behavior Genetics” by J.L. Fuller and W.R. Thompson in 1960 marked the beginning of behavioral genetics discipline. However, it has a long past, in which the role of genetical traits was also seen. For example, the ancient Greek supposed that humans inherited qualities from their ancestors. The ideas referring the heredity or non-heredity of behavior were present in other periods of ancient times, as well. The modern form of the debate roots to the periods of the seventeenth to the nineteenth centuries. In those days, there were two firm opinions concerning the impact of genes onto anyone’s behavior. Some experts believed that people are destined to conduct themselves to a great extent in the way their parents do. The idea of the prevalence of hereditary over environmental factors in forming a person’s behavior was inherent in one group of scientists. This group was known as “nature school of thought,” since it was considered that each person has become certain genes from nature and their traits cannot be escaped. The other scientists took a different view on the origin of particular behavior. They belonged to the “nurture school of thought,” whose conviction was that the children were not prone from birth to any destined forms of behavior. According to this school’s teachings, the environment that surrounds a child during its growing up makes the most important effect on that kid’s behavioral patterns. Nowadays, however, most analysts agree that both environment and genes influence forming behavior. The first scientist who coined the expression “nature and nurture” was Francis Galton (1822–1911). In his research he investigated the families of outstanding men and came to the conclusion that mental powers run in families. As one of the first behavioral geneticists, Galton advocated for improving the genetic quality of the human population through increasing the birth rates among people with desired traits. Sterilization or reducing reproduction was purposed to be applied in people who had undesired traits. Interestingly, Galton’s theory was believed to act as a motivator in Hitler’s total extermination of the Jews during World War II. Another research worker in the science of heredity of that time was Mendel (1822- 1884), whose experiments “revolutionized our understanding of genetics”. Through the set of procedures with the plants, he founded that children receive genes from the parents in a precise form. But, those genes take different forms in the offspring, thereby specifying diverse representations of the trait. In 1920s, the followers of Galton’s and Mendel’s studies began the first human behavioral genetic testing on mentality and diseases of the mind. Nowadays, the research on human behavior focuses on detecting specific genes, which influence behavioral features, such as intelligence and personality, and diseases, such as depression, autism, schizophrenia, and hyperactivity. Thus, many studies expose that there is an evident link between schizophrenia and genetic background. This disease leads to altered behavior. Offspring whose both parents have schizophrenia is 46 percent likely to have the disorder as well. However, it is proved that an adopted child whose new mother or father has schizophrenia falls under the risk of showing schizophrenic symptoms. As follows from the described phenomenon, an environment also plays a role in an evolvement of the illness. Such behavioral disorders as alcoholism and depression are regarded to have also the both genetic and environmental influence sources. Not less interesting is the exploration of “genetics” of cleverness or aggressive behavior. Through their experiments, the geneticists have found that adoptive children, but not their adoptive ones, usually resemble their biological parents in intelligence. This fact confirms the theory of hereditary impact on mentality. However, it is also proved that the way of nurture in the family, the culture, and education determine almost half of the child’s intelligence. If speaking about the correlation between aggressive behavior and inheritance, it should be admitted that the “nature and nurture” formula is relevant in this case as well. The scientists have extracted genes associated with a predisposition to criminality. These are the MAOA gene (monoamine oxidase A) and a variant of cadherin 13 (CDH13). The MAOA gene is critical for regulating the quantity of serotonin and dopamine in the brain. CDH13 is linked with substance abuse, attention deficit/hyperactivity disorder (ADHD), and schizophrenia. These genes may complicate the ability to control violent performances, but they do not predetermine someone for criminality. To confirm the previous statement, the authors of “The Human Genome” indicate that MAOA, by itself, does not predict aggressive and violent behavior, unless environmental factors are engaged.

In the previous paragraph, it was said a few times that scientists came to conclusions in behavioral genetics through some experiments and tests. Indeed, it is curious to know what methods and tools they use to understand the functioning of a gene. Thus, methods of genetic research on behavior include approaches based on the principles of epidemiology, molecular genetic technology, and animal studies. There are two quasi-experimental methods that are relevant to genetic epidemiology: twin studies and adoption studies. Through the twin method researchers observe the behavior of identical and fraternal twins with the help of interviews and personality tests. Twin studies bank on the fact that identical twins have actually the same array of genes while fraternal twins have, for the most part, a half-identical set. Adoption studies look at people related by blood who have been grown apart. Adoption method supposes that analysts compare identical twins adopted in separate families, make comparison of adopted children to both their adoptive and biological parents, or compare adoptee to other children in the family who are biological offspring of the parents. One of the examples how the adoption method has given recognition to the genetic origin of some behavioral disorders is the research provided in 1966 by American geneticist L. Heston. The work presented that kids that were adopted away from their biological schizophrenic mothers experienced the same risk level to become schizophrenic as did the children nurtured by their schizophrenic biological mothers. Methods of molecular genetic technology include linkage analysis, association studies, and microarray analysis. Under linkage, scientists understand monitoring families’ variables, such as traits and genetic markers. Association study focuses on a single gene that has been isolated. DNA samples are taken from people who have a certain trait and those without it. Then the availability of alleles is compared in both cases in order to trace the genetic component in the nature of conduct. Microarray analysis involves placing of a human’s genome into a chip. Then the chip should be soaked into ribonucleic acid fluid. The particular segment will get radiant if a particular gene is expressed in the cell. The technique known as knockout study has been applied to animals. The researchers deactivate a gene in stem cells, which then will be placed into the womb of a female. After the birth of the offspring, its germ cells will be inspected. The knockout mice are compared to untreated mice with a view to behavior in order to ascertain that the alterations in it have occurred due to implication of the gene.

The techniques, such as twin or adoption study have made a significant contribution in the development of behavioral genetics. However, the discoveries in this field should not be exaggerated. It can not be said that any separate gene bears total responsibility for alcoholism or sexual orientation, for example. The truth is that the environmental stressors have significant influence on behaviors, as well. Another challenge is that the knockout method cannot be safely applied in the human. The effects of the missing gene in the development of the organism can be unpredictable. Despite this, microarray technique is considered more promising. The detecting enzymes through fluorescent protein can allow scientists to observe changes in gene expression as they occur. Through this method, geneticist can make one step closer to discovering how neurons’ transformation that was generated by interactions between the environment and genes, give rise to behavior.

Hopefully, some day doctors will be able to propose the ways of curing or preventing genetic behavioral diseases by supplementing or replacing faulty genes. The gene revolution could put an end to much human suffering and could make the twenty first century better for everyone.

In conclusion, it is worth to emphasize that behavioral genetics is the branch of science, which calls a genuine interest in the researchers due to the complexity and intricacy of its solving. As it is declared in this paper, the mission of genetics is to identify which features are inherited, and explain how these features pass from generation to generation. For this purpose, the scientists do researches on the human genome, since it results in the formation of posterity’s traits. The trials of finding the genetic explanations of abnormal or antisocial types of behavior have been made long before our days. The historical survey of this paper helps the reader have a closer look at the development of genetic studies. The geneticists of our century came to the conclusion that both the genes and the environment have an influence on the heredity. Methods and techniques, such as twin study, adoption method, knockout of the gene were the most helpful to the geneticists in their work. The microarray analysis remains the most promising for further researching in this area.

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