Genetics and Behavior PDF

Genetics and behavior Genetics is the study of heredity-the inheritance of physiological or psychological traits. Genetic research is based on the principle of inheritance (patterns of behaviors can be inherited)  One’s genetic material exists in the form of DNA. Genetic information is c...

Genetics and behavior Genetics is the study of heredity-the inheritance of physiological or psychological traits. Genetic research is based on the principle of inheritance (patterns of behaviors can be inherited)  One’s genetic material exists in the form of DNA. Genetic information is contained in chromosomes, which are tightly wound strings of DNA present in every cell of human body. Genes are groupings within the DNA of any chromosome. There are 23 pairs of chromosomes in every human cell (except egg cell and sperm) – each inherited by each parent. These pairs have approximately 20000-25000 genes. We now know this through the completion of the the human genome project which started in 1990 with the goal to map and sequence the genetic make-up of the human species by identifying the 25000 genes→ completed in 2003. This was an important step in explaining behavior and developing treatments but still role of specific genes in specific behavior unknown.  Alleles are different forms of the gene: can be dominant or recessive. The trait controlled by the recessive allele only develops if the allele is present in both chromosomes in the pair (e.g. blue eyes allele), whereas the trait controlled by the dominant allele will develop if at least one of the chromosomes in the pair contains it (for example brown eyes allele).  Genes are thought to be responsible for the development of physical and behavioral characteristics. The genetic make-up of an individual is called their genotype. However, it has been known that the genotype does not exclusively determine the characteristics of an individual. A number of environmental influences such as diet, habitat also influence the way an individual organism develops. M.Foteinopoulou   The characteristics of an organism that manifest is called the phenotype (e.g. eye color, height, blood type, immune system and behavior). The phenotype is the result of genotype and environment interacting.  Behavioral genetics deals with understanding how both genetics and environment contribute to individual variations in human behavior. Psychologists argue that an individual may inherit a genetic predisposition towards a certain behavior, however, without the appropriate environmental stimuli this behavior may not manifest or be expressed (e.g. diathesis stress model). For example, DSM to explain origin of depression – genetic predisposition to depression but exposure to environmental stress –more likely to express depression. This explains why not all people develop depression after a traumatic event. It also illustrates the complexity of the matter and that there is no single cause and effect relationship between genes and behavior. →Bidirectional relationship –they influence each other.  Also accepted that it is not probable that a single gene is responsible for complex behaviours as intelligence, criminal behaviour, altruism or attachment. Instead, what is inherited may be the building blocks for such complex behaviours.  One of the major controversies in the history of psychology is the nature vs. nurture debate, in which researchers debate whether human behavior is the result of biological or environmental factors. It is now recognized that both play a role and the question is to what extent each contributes. METHODOLOGY in Genetic research Genetic research mostly relies on correlation studies which establish that there is a relationship between the variables but no cause and effect can be determined. They use these studies to study the possible correlation of genetic inheritance and behavior by calculating the concordance rate – the probability/likelihood that if 1 individual has the trait the other will also have it. It is assumed to establish if and to what extent a certain trait is inherited. Types of correlational studies usually used in genetic research (based on genetic similarity) →twin studies, family studies (Kinship studies), adoption studies. M.Foteinopoulou These studies are based on the genetic similarity principle. Psychologists use these different degrees of genetic relationship as a basis for their hypotheses about the contribution of genetic and environmental factors to behaviors such as psychiatric disorders or addictive behaviour. It should be the case that the higher the genetic relationship, the more similar individuals will be if the particular characteristic being investigated is inherited. - Twin research Identical twins (monozygotic twins MZ) are 100% genetically identical as they have developed from the same egg. They therefore act as a control for each other. Fraternal twins (dizygotic twins DZ) have developed from two different eggs. They share around 50% of their genes, so they are no more similar than siblings. The higher the genetic relationship the more similar the individuals should be if the particular characteristic investigated is inherited.→ So, in twin research sets of MZ are compared to sets of DZ twins for a particular trait or disorder. High concordance rates in MZ and lower concordance rates in DZ for the same behavior indicates that the trait or disorder is linked to genes (inherited). If the concordance rate is high for both MZ and DZ twins it is may be assumed that environmental factors play a large role in the observed behavior. It makes sense for psychologists to first carry out twin studies to determine the concordance rate for a behaviour between twins before carrying out more sophisticated genetic research, which is much more expensive. But twin research has some limitations:  Twins tend to experience a very similar environment while growing up. Therefore, it is difficult to isolate environmental influence as a variable.  But, we also have to be careful not to overestimate the similarity of the environment for both twins. Assuming that twins grow up in equal environment is often called the equal environment fallacy. Some research suggests that parents, teachers, peers and others may treat identical twins more similarly than fraternal twins.  Finally, twins are not highly representative of the general population, so it is difficult to generalize the findings. M.Foteinopoulou  - Family studies Another way that behavioral genetics is studied is through family studies (kinship). Unlike twin research, this is a more representative sample of the general population. Ordinary siblings will share 50% of their genes, grandparents will share 25% of their genes with their grandchildren and first cousins will have 12.5% of their genes in common. Thus, family studies allow the comparison of different degrees of genetic relatedness and occurrence of a behavior. (Example IQ- stronger correlation between mother and child and weak correlation between second cousins.) If a behavior is suspected of being genetic within a family, psychologists use prospective studies: the sample is selected and observed before certain behaviors are observed (instead of relying on family history). The researchers watch for outcomes, such as the development of a disorder. E.g. individuals who are considered “genetically vulnerable” for schizophrenia can be followed over many years to see if they actually develop the disorder. But: ethical concern that such research may cause undue stress when labeled as vulnerable. Although family studies indicate a potential genetic link to behaviour, there is no genotype studied – so it is not possible to determine if a specific gene might be responsible. In addition, family studies do not control for environmental factors. - Adoption studies Allow the most direct comparison of genetic and environmental influences of behavior. These compare adopted children to their adoptive parents, biological parents, adoptive siblings and biological siblings. We can infer genetic influences if adopted children are more similar to their biological parents than to their adoptive parents. On the other hand, if the environment has the strongest role to play, the reverse pattern should be found. Criticisms: that these children are not representative of general population and also that adoption agencies tend to use selective placement when finding homes for children, trying to place children with families who are similar in as many ways as possible to the natural parents. Consequently, the effects of genetic inheritance may be difficult to separate from the influences of the environment. M.Foteinopoulou   Overall, these approaches to the study of the relative influence of genetic make- up and the environment allow researchers to determine if there is a potential genetic origin of behaviour. In spite of the weaknesses outlined here, it is clear that there is a correlation between several behaviors and genetic inheritance. With the advancements of modern technology and the human Genome Project more sophisticated research in behavioral genetics can be conducted. - Genetic mapping: Genetic mapping (also known as linkage analysis) is use to identify the alleles of particular genes in a particular individual. To create a genetic map, researchers collect blood samples from members of the families in which a behaviour is common – for example, schizophrenia or aggression. The researchers examine the DNA for polymorphism – the presence of genetic variation. These polymorphisms are referred to as genetic markers. Genetic variants are then correlated with observed behavior. These methods are usually used to identify specific genes responsible for specific behavior—e.g. the “gene of depression”, “gene of aggression”. (genetic mapping – looking for genetic variations – identify genetic markers). Association studies look to see if there is a correlation between these genetic markers and a certain behaviour. Although this is much more precise than the general twin study research outlined above, the results are still correlational in nature. There would have to be a lot of research on these markers in order to see whether the effect is significant. That is where GWAS come in. Once a particular gene is suspected of playing a role in human behaviour, researchers today carry out Genome-wide association studies – known as GWAS. These studies compare the DNA of two groups of participants: people with the behaviour and similar people without, who serve as controls. If a genetic marker is more frequent in people with the behaviour, it is said to be "associated" with the disorder. As you can see by its name, GWAS by definition is a very large study – often using data from hundreds of thousands of samples of both control and “target behaviours.” By using such a large amount of data, the effect of outliers does not lead to false conclusions. M.Foteinopoulou SUMMARY: Ways that researchers study genetics Twin studies: Researchers compare behavioural traits of monozygotic (MZ or identical) twins and dizygotic (DZ or fraternal) twins to evaluate the degree of genetic and environmental influence on a specific trait. Family studies: Researchers trace a phenotype over several generations in a family tree to determine the likelihood that a behaviour is inherited. Adoption studies: Researchers investigate similarities between the adoptee and their biological and adoptive parents. Similarity with the biological parent is potentially the result of genetic inheritance, while similarity with the adoptive parent is more likely the result of environmental factors. Linkage analysis: Matching genetic variations (polymorphisms) with the frequency of a behavior. Genome-wide Association Studies: an examination of a genome-wide set of genetic variants in a large sample individuals to see if any variant is associated with a trait. Inthinking, Crane M.Foteinopoulou