The behavioral genetics discipline deals with the genetic factors affecting human behaviors. It deals with the formation of behavior with respect to the purview of psychology and psychiatry. These traits may involve cognitive impairments, mental illness, depression, aggression, schizophrenia, substance use, and behavioral problems. Further, behavioral genetics in the light of technological advancement became an important tool in discovering the alleles and genes responsible for the behavioral characteristics of humans.
Meanwhile, as environmental conditions provided by the parents and shaped by the society hone individuals to maximize their innate or inborn potentials, the similarities on the growth and developmental patterns among relatives illuminate the effects of their inherited genes. While the genotype dictates the possible occurrence of a particular behavior, the nature shapes the phenotypic behavior that will be expressed.
In relation to this, although most developmental psychologists have taken into consideration the hereditary influences in the development of cognitive skills, mental abilities, and multiple intelligences on every individual, still they believe that environmental conditions take prevalence in molding ones’ personality. As such, experts are in continuous search for the genes responsible for the development and inheritance of various diseases and personality disorders.
Charles Darwin, the proponent of the “natural selection” theory, was influenced by Francis Galton in relating the biological basis of evolution to behavioral characteristics of animal species (Plomin, Owen, and McGuffin, 1994). The variation on the expression of behavioral attributes of organisms under specific type of species can be attributed to genetic changes. These variations can survive and further change in the succeeding generations of that species (Plomin, Owen, and McGuffin, 1994). For instance, curiosity can be observed in every animal species.
Some animals display high level of curiosity than other animal group which projects their survival mechanism. In connection to this, the discipline of behavior genetics is an intensive application of the biological basis of behavior that generally aims for the determination the variation extent of specific trait in a given population of organisms (Plomin, Owen, and McGuffin, 1994). Specifically, it examines both genetic and environmental influences on the trait variation as well as the interactions between heredity and the environment.
Behavior genetics is also concerned on the genotype or the underpinning genetic structures in specific behavior (Plomin, Owen, and McGuffin, 1994). In fact, the experiments on animal selective-breeding undeniably showed the influence of hereditary traits in the behavior of different animal species. Behavioral and Medical Genetics The behavioral genetics discipline deals with the genetic factors affecting human behaviors while medical genetics encompasses the exerted influence of the genes on complex behavior (Parens, 2004).
Medical genetics includes genetic factors which influence behavioral trait formation with respect to the purview of medicine such as hypertension, cancer, and diabetes (Parens, 2004). On the other hand, behavioral genetics deals with the formation of behavior with respect to the purview of psychology and psychiatry (Parens, 2004). These traits may involve cognitive impairments, mental illness, depression, aggression, schizophrenia, substance use, and behavioral problems. As well, the demarcation between behavioral and medical genetics is not fully-defined (Parens, 2004).
For instance, depression cases which originally classified under the purview of psychiatrists and psychologists are now held by medical doctors. Similarly, the scope of medical researches like Alzheimer’s disease nowadays is also concerned of psychologists. Although, the names of these two endeavors are different, the molecular approaches, methodological and research questions are principally similar. Genetic Influences At present, most of the experts in behavioral genetics utilize the molecular methods of researchers in medical genetics (Parens, 2004).
Both groups employ DNA-based technology to unravel the genetic mystery and the disorder or the behavioral traits. It is important to understand this primary goal of the study prior to the selection of the molecular method of the study. Researchers in behavioral genetics are using classical, epidemiological, and quantitative methods of study (Parens, 2004). For example, the twin studies fall under the classical methods while the DNA-based methods are classified under molecular-behavioral methods.
Meanwhile, the experiments on behavioral genetics were conducted not only in microorganisms but also in insects like houseflies, mosquitoes, bees, fruit flies, crickets, wasps, moths and even in cows, fishes, dogs, geese and other animal species (Plomin, Owen, and McGuffin, 1994). The artificial selection or selective-breeding of these organisms resulted to conclusive relationship between behaviors and genetic processes. On the other hand, the genotype-environment interactions were assessed by natural behavioral observations on organisms in a defined environmental condition (Plomin, Owen, and McGuffin, 1994).
For example, the observations made by early psychologist on the stimulus-conditioned response among animals have contributed in the understanding of human learning. In relation to this, in genetic studies, animals have crucial roles, serving as models for the experiment. For instance, a mouse model that was deficient in HRPT enzyme was genetically engineered in the laboratory so as to understand the human case of this deficiency. The HPRT deficiency, ascribed with a recessive X-linked gene, is associated with Lesch-Nyhan syndrome (Gershon and Reider, 1992).
This genetic disorder was correlated with mental retardation and self-injurious behavior through animal studies (Gershon and Reider, 1992). Further, animals are also utilized as models for several neurobehavioral disorders such as epilepsy, alcoholism, and narcolepsy. In this view, animal models, through experiments, serve as means to gain understanding on the nature and occurrence of genetic disorders as well the exploration on the prevention and proper medical treatment. In every animal study, it is generally assumed that the underlying genetic principle works similarly among organisms.
Moreover, in the advancement of genetic technology, locating, characterizing, and identifying genetic variation through genes is now possible. Methods in Behavioral Genetics Inbreeding Mice are typically used in inbreeding experiments. Inbreeding is done on animals in order to generate a genetically identical, homozygous population. Approximately after thirty generation, 98-100% homozygous organisms can be produced (Parens, 2004). Since the subjects of the study bear the same genes, the variation then on their respective phenotypic behavior is directly caused by environmental variables.
Twin Studies Inbreeding is not done in humans for genetic traits of the humanoids can hardly be manipulated. Thus, twin studies are of prime importance in dealing with genotypic and phenotypic experimentations. While the identical or monozygotic twins are genetically identical, the fraternal or dizygotic twins are more genetically identical than normal siblings (Parens, 2004). The shared traits among identical and fraternal twins and non-twin individuals are significant for comparison and contrast.
If identical twins have more behavioral traits than fraternal twins, genetic influences then interceded. Both identical and fraternal twins, although shared differently in the inherited traits, experience similar pre-natal environment, thus, the genetic factors can be isolated for behavioral assessment (Parens, 2004). On the other hand, the genetic make up of fraternal twins are entirely different from non-twin individuals. Also, non-twin siblings have different pre-natal environment, hence, giving opportunity for comparison based on environmental factors (Parens, 2004).
Knockout Studies In knockout study design, genes are either inserted or cut form the embryonic cells of mice (Parens, 2004). This is done to control and manipulate the genetic characteristic of the subjects. Then, they are reinserted into a female for gestation. Most knockout studies employed on and off gene mechanism through drug treatment or antibiotic (Parens, 2004). The researcher can turn the gene on or off by the combination of the deleted or inserted gene with a particular gene susceptible to drug treatment. Molecular Biology
Genetics and the advent of molecular biology have brought valuable insights into the inheritance of both genetic and behavioral disorders. For instance, it was identified that chromosomal aberrations resulting to an extra chromosome 21 would cause mental illness in Down syndrome cases (Carson and Rothstein, 1999). Likewise, the gene responsible to various single-gene diseases with mental retardation accompaniment has been identified including their respective complications. Hence, new born screening is implemented nowadays for early detection and medication of metabolic or genetic disorders.
Generally, behavioral and biological connections with respect to chromosomal aberrations are easier to determine than the complexity of the normal behavioral patterns (Carson and Rothstein, 1999). Contemporary technology on genetic studies is employed on single-gene treatment along with its behavioral characteristics. For example, DNA from either affected or unaffected population is analyzed in the identification of the culprit gene for the observed behavioral defects (Plomin, Owen, and McGuffin, 1994). After gene identification, the allele responsible for neurological problem is then determined.
Similarly, gene mapping technique or linkage analysis is applied in the identification of the chromosomal position of a specific gene. Then, the DNAs of both affected and unaffected individuals from different families are analyzed to determine the link between a gene encoded in the DNA or marker and the occurrence of the genetic disorder (Plomin, Owen, and McGuffin, 1994). In connection to this, it is commonly postulated that high association entails the chromosomal closeness of the link between the DNA marker and the disorder.
Heredity and the Environment
Specific organisms sustain existence in different environmental conditions as both environment and genes control and direct their growth and development (Scarr, 1992). Thus, it is possible to attribute behavioral observations to genes or environmental factors. Further, the relative influences of environment and heredity as well as their interactions can possibly ascribe with the characteristic variation among members of a population (Scarr, 1992). In genetic studies, twins are typically used for behavioral analysis and comparison.
The research on the behavioral developments of identical and fraternal twins, under identical social conditions, is one strategy employed to assess heredity-environment relationships. Likewise, hereditary and environmental influences are also examined by means of the behavioral comparison and contrast among unrelated individuals grown in the same custody like in the case of adopted children. By this method, similarities on the behavioral traits of the subjects would directly ascribe to environmental factors for they are entirely different with respect to genes (Plomin, Owen, and McGuffin, 1994).
Furthermore, quantitative methods like biometric technique facilitate the processing of various family genetic-environment data (Plomin, Owen, and McGuffin, 1994). Experts attributed the behavioral phenotype differences among individuals to their inherited genes from their respective parents in parallel with the nurturing environment. However, the difficulties in the identification of environmental factors involved in behavioral nurturing are even greater than in the determination of the genes responsible for the phenotypic behaviors.
On the other hand, both theoretical and technological advancement along with the conventional techniques provide great help in the study of hereditary-environmental behavior determinants (Plomin, Owen, and McGuffin, 1994). Meanwhile, heredity has been correlated with the variation of intelligence; the nature and transmission of genes is a strong predictor of intelligence. In fact, as estimated, about 40-70% of intelligence variation can plausibly explained by hereditary traits (Plomin, Owen, and McGuffin, 1994).
As revealed by more than five decades of research on the intelligence of related individuals, identical twins grown separately are just similar to adopted individuals brought up in the same custody (Scarr, 1992). While identical twins grown up together are much similar as compared to fraternal twins brought up in the same home, the reared identical twins are much similar than adopted individuals grown in the same custody (Scarr, 1992). Experts in the behavioral genetics discipline argued for the genetic basis of human behaviors such as aggression, depression, impulsivity, homosexuality, and substance use.
This scientific search for the genetic basis of behavior led to the reemergence of behavioral genetic determinism bearing the notion that behaviors are largely shaped by genetic processes (Carson and Rothstein, 1999). On the other hand, researches on twins and adopted individuals were the traditional studies conducted to differentiate environmental and biological influences in personality formation (Carson and Rothstein, 1999). Recently, researchers have looked into the DNA parts or genes which probably cause mental health problems like bipolar disorder and schizophrenia, and even depression.
However, specific gene responsible for the occurrence of these disorders was failed to be identified (Carson and Rothstein, 1999). Also, genetic expert were not able to relate basic personality attributes and sexual preferences to any gene. Meanwhile, although some displayed behavior can only be attributed to a single gene, most of the expressed behaviors were generated by several genes or polygenic influence (Parens, 2004). In addition, environmental variables intercede on the genetic influences in behavioral expression resulting to the convolution of the scenario.
Hence, for the analysis of genotypic and phenotypic behavioral interrelations, researchers formulated the scale of heritability with zero to one value-range (Parens, 2004). The heritability values are projections of variance measures expressed in the trait due to inheritance. As such, the zero value denotes that the phenotypic behavior is entirely independent from the behavioral gene while the value of one is an indication that the phenotypic behavior is absolutely attributed to the inherited gene.
Analysis and Conclusion
The aforementioned findings of behavioral studies proved that genetic processes are directly responsible for human growth and development. Meanwhile, as environmental conditions provided by the parents and shaped by the society hone individuals to maximize their innate or inborn potentials, the similarities on the growth and developmental patterns among relatives illuminate the effects of their inherited genes (Scarr, 1992). For example, identical twins grown in different custody have similar traits just like twins brought up in the same family.
In relation to this, although most developmental psychologists have taken into consideration the hereditary influences in the development of cognitive skills, mental abilities, and multiple intelligences on every individual, still they believe that environmental conditions take prevalence in molding ones’ personality (Scarr, 1992). Similar to this, as adoption, twin, and family studies showed the genetic influences in the inheritance of depression and schizophrenia, the role of environmental variables is crucial in the development of personality traits.
As such, experts are in continuous search for the genes responsible for the development and inheritance of various diseases and personality disorders. For instance, psychopathological data gathered for a number of years revealed the genetic factors in the alcoholism and other substance use. In fact, alleles which corresponds for the alcohol-metabolizing enzymes, dehydrogenases like aldehyde dehydrogenase were variedly detected among nonalcoholic and alcoholic Chinese men (Plomin, Owen, and McGuffin, 1994).
However, conclusive findings concerning gene that is specifically related to alcoholism was hardly produced. It was postulated that alcoholism has complexity which may not only involve a specific gene but also includes synergism among genes and gene-environment interactions. Behavioral genetics in the light of technological advancement became an important tool in discovering the alleles and genes responsible for the behavioral characteristics of humans (Parens, 2004).
This discipline has triggered the issues concerning the basis of behaviors; people contended on the genetic explanation for the exhibited behavior as they generally believed on the notions of nature and nurture assumptions. However, the nature and nurture notions, even though may play a significant role in behavior determination, as predictors of behaviors have limited view on behavior acquisition and modification (Parens, 2004). While the genotype dictates the possible occurrence of a particular behavior, the nature shapes the phenotypic behavior that will be expressed.
As compared with the Mendelian genetics, behavioral genetics is much complicated for the pea plant used by Gregor Mendel in his experiments directly showed the characteristic variation while animal or human behaviors can hardly be interpreted as they way it was exhibited (Parens, 2004). Thus, the successful association between genes and behaviors is attained when the genotypic behavior concurred on the phenotypic or observed behavior. In such way, the behavioral genes can be identified and the extent of its behavioral expression can be further determined.
References: Carson, R. A. and Rothstein, M. A. (1999).
Behavioral Genetics: The Clash of Culture and Biology. Baltimore: Johns Hopkins University Press. Gershon, E. L. and Reider, R. O. (1992). Major Disorders of Mind and Brain. Scientific American, 267(3), 126–133. Parens, E. (2004). Genetic Differences and Human Identity: On Why Talking about Behavioral Genetics Is Important and Difficult. Garrison, New York: The Hastings Center. Plomin, R. , Owen, J. , and McGuffin, P. (1994). The Genetic Basis of Complex Human Behavior, Science, 264, 1733–1739. Scarr, S. (1992). Developmental Theories for the 1990s: Development and Individual Differences, Child Development, 63, 1–19.