Describe genetic similarity in the study of human behaviour

Introduction to the approach

The biological approach argues that there are physiological origins of many behaviours and that human beings should be studied as biological systems. Biological approach studies behaviour as a result of genetic and other biological explanations.

Introduction to the topic

A gene is a unit of heredity, a certain region of the DNA encodes for a certain trait or function. For example, eye colour, height, etc. Human DNA consists of 23 chromosomes, 20,000 genes and 3 billion base pairs. The set of traits coded in an individual’s DNA is called a genotype. The set of traits that actually manifest in an individual’s body, appearance or behaviour is called phenotype.

Introduction to the subtopic

There is a significant body of research that supports that MDD has its roots in biology. The study of twins can be used to understand the relative influence of genes versus environmental causes. MZ twins share all their genes whereas DZ twins only share about half. Therefore, any significant difference between MZ can be attributed to environmental factors. Genetic similarity is referred to as relatedness and it is assumed the greater the genetic similarities between two or more individuals , the higher the degree of relatedness.

Kendler el al (2006) - Aim

• Study type: Twin study using data from over 42,000 twins in the Swedish National Twin Registry.

• Aim: To determine the level of heritability of depression.

Kendler el al (2006) - Research Goals

1. Replication: To test whether previous findings on the heritability of major depression could be replicated in a large, representative twin sample.

2. Sex differences: To investigate whether genetic influences on depression differ by sex, specifically whether heritability is stronger in females than in males.

3. Cohort effects: To examine whether heritability varies across historical cohorts, testing the idea that heritability depends on population and time period, rather than being a fixed characteristic of the disorder.

Kendler el al (2006) - Method

Data collection was performed with a telephone interview by trained interviewers. Introductory letters describing the study were also sent to a random sample of which finally 42000 participants’ data was analysed. Informed verbal consent was obtained prior to the interview and it was approved by the ethics committee.

Kendler el al (2006) - Results

In this large, nationally representative twin sample the heritability of major depression was estimated to be 38%. These results are in close agreement to those obtained previously from a meta-analysis of the methodologically rigorous twin studies of major depression, which estimated, across studies, that heritability of major depression was 37%.

Link

These results provide strong support for the hypothesis for genetic similarities shared between MZ twins which increases the concordance rate of depression. The proportion of population risk in major depression attributable to genetic factors appears to be moderately greater in women than in men.

Conclusion

In conclusion, it can be said that patterns of behaviour are inherited and genetic similarities do exert an important influence on human behaviour. While the nature- nurture debate is ongoing and the studies also suggest an interaction of the two factors, it can definitely be asserted that genetic make increases the vulnerability of depression