Behavioral Genetics: Twin and Family Studies

Introduction:

Genetics is the branch of biology that deals with the study of heredity and genetic materials like DNA. This is a complex branch as every individual expresses varied traits. Still, these studies help determine the uniqueness and similarities of the individual's behaviors. Genetics can be divided into various branches, and behavior studies are one among them. Behavioral genetics studies determine the traits among families and twins and the influence of genes and environment on them.

What Is Behavioral Genetics?

Behavior genetics, popularly known as psychogenetics, is the study of genes' role in a person's behavior and characteristics. Gerald E. McClearn, the father of behavior genetics, first described this concept. Behavioral genetic research aims to estimate the role of genetic and environmental factors contributing to behavioral variability in the population under study. Traditional behavioral genetic methods primarily use family, twin, and adoption correlations to estimate the relative contributions of genetic and environmental influences in the etiology of individual differences. Behavioral genetics is summarized under the following laws.

• First Law: All human behavioral traits can be inherited.

• Second Law: The effect of family background is less than genes.

• Third Law: Some portion of genetic variation is not attributed to the effect of any genes or families.

How Are Behavioral Genetics Studied?

Quantitative genetic methods are used to estimate the net effect of genetic and environmental factors on individual characteristics, including behavioral traits. Molecular genetic methods are used to identify specific genes responsible for genetic influence. Behavioral traits of humans and animals are closely studied. The results obtained are more accurate in studies including animals, as their genes and environments can be altered in the laboratory during the studies.

In humans, as true experiments cannot be carried out, the analysis is done based on a quasi-experimental design that uses the previously collected data.

What Are Twin Studies?

Twin studies are the research methodology used by researchers to determine the traits and behaviors in identical and non-identical twins. Twin studies remain one of the best ways of identifying genetic markers linked to complex behavioral traits. This is considered one of the most important types of research in behavior genetics. The first reported twin study was performed by Walter Jablonski in 1922; later in history, many twin studies were carried out. One of the renowned twin studies is the one performed by Thomas J. Bouchard, Jr. and his colleagues in 1990. In this study, two identical twins were separated and grew up in two different cultural backgrounds, but later when their behavioral patterns and traits were studied. The researchers observed the following common among the twins:

• Both married and divorced.

• The name of the first wife of both was Linda.

• Both married again to a woman called Betty.

• Both took up police training.

• Both had identical drinking and smoking habits.

• Both named their pets Toy.

• Both had a habit of chewing fingernails.

• Both named their son James.

It was found that both had many similarities, like twins who grow together in the same environment. This study has been evidence of the theory that genetic material plays an important role in developing traits and behaviors. Twin studies that can be carried out today are done on twins who grow up in the same environment; adoption and separation of the twins are not permitted anymore.

What Are the Advantages of Twin Studies?

• Twin studies present evidence of shared genetic and environmental factors for any particular trait of interest.

• It helps determine the effect of genes and environmental factors in determining a particular trait.

• The use of twins can improve the statistical power of a genetic study by reducing the amount of genetic and environmental variability; the extent to which different assumptions matter may depend on which trait is being studied.

What Are the Limitations of Twin Studies?

• As the sample studied is not randomized, results from twin studies cannot be directly generalized to the general population.

• Some researchers state that genetic factors can lead to a higher incidence of female twin births.

• Though genetic studies are advancing rapidly, twin studies still follow the same line of study and analysis as they followed back in 1920. Most of the previous assumptions are considered inaccurate today.

• The data collected from twin studies are often misunderstood, misinterpreted, and misplaced by the media and even by researchers.

• Twin studies are based on voluntary participation, therefore, can include selection bias.

• The use of twins does not allow the researcher to simultaneously consider the effects of both shared environment and gene or environment interaction. This can be addressed by including additional siblings in the design.

What Are Family Studies?

Family studies are fundamentals of behavioral genetics. These studies were described by Turner, Cardon, and Hewitt and are of great importance for behavioral medicine. These studies assess the families' physiological, physical, and psychological similarities. Family studies are commonly carried out in cases with ADHD; These studies do have many advantages over twin studies. In family studies, researchers examine the patterns of similarity and differences in behavioral traits among family members, such as siblings, parents, and offspring. By comparing these traits within and across different types of relatives, researchers can estimate the heritability of specific behaviors, which refers to the proportion of phenotypic variation that can be attributed to genetic factors.

There are three main types of family studies in genetics:

1. Studies that measure the degree of familial aggression for a particular trait.

2. Linkage studies are a genetic means to determine the loci that are responsible for the disease or any trait expressed.

3. Association studies are the methods that determine the loci with less effect on the expression of genetic conditions.

Conclusion:

Behavioral genetics or psychogenetics is a branch of science that deals with determining the role of inheritance and genetic factors in expressing certain traits and behaviors of a person. It also analyses the role of the environment and family in the upbringing and development of the child. These studies do have many limitations and drawbacks. Randomization is not done while selecting the sample; they have voluntary samples, a small sample size, and the study depends on previously collected data. But still, the results and conclusions obtained from genetic research have proven beneficial in understanding the role of genes in expressing certain characteristics.