Behavioural genetics

Behavioural genetics is about studying the link between genetics and psychological characteristics. It is associated with the nature vs nurture debate. Whilst the name connotes a focus on genetic influences, the field broadly investigates genetic and environmental influences.

Human study designs:

• estimating the degree of genetic and environmental influences using family, adoption and twin studies. 
• identifying genes associated with behaviour by using case control studes
• gene environment interplay: interaction and correlations

We inherit our genes from our family, meaning that we share a percentage of our genes with our kin. Identical twins (monozygotic) share 100% of their genes. Non-identical twins (dizygotic) share 50% of their genes, the same as parents, and full siblings.

Family studies show whether traits or disorders run in families. Gottesman's (1991) classic study on schizophrenia and inheritance showed that there was a far higher chance of developing schizophrenia if someone related to you also had it. Monozygotic twins had a 48% chance risk if one of them had it. This is in comparison to only 1% risk to the general public.

If characteristics run in families, it suggests that there may be some genetic contribution. However, we don't inherit just our genes from our family, but also our environment.

Adoption studies

• Adoption is a legal process whereby a child becomes part of, and raised by a new family. They may have no biological relation to the child
• These studies are used to estimate the degree to which a trait varies in response to environmental and genetic variation
• Similarity with the biological parent is expected to be heritable genetic effect, whilst similarity with the adoptive parent is associated with home-environment, called the shared environmental effect
• The familial method compares non-biological siblings who are reared in the same household. Similarity to non-biological siblings raised in the same household is attributed to shared environment effect, as the siblings are biologically unrelated, but share the same home environment

• Twin studies estimate genetic and environmental architecture of a behaviour/condition. They reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders
• Twins are a valuable source for observation because they allow the study of environmental influence and varying genetic makeup: monozygotic twins share nearly 100% of their genes, which means that most differences between the twins (such as height, intelligence, depression) are due to experiences that one twin had but not the other twin
• Dizygotic twins share only about 50% of their genes, the same as any other sibling
• Twins also share many aspects of their environment because they are born into the same family. The presence of a given genetic trait in only one member of a pair of identical twins provides a powerful window into environmental effects
• The classical twin design compares the similarity of MZ and DZ twins. If identical twins are considerably more similar than DZ twins, this implicates that genes play an important role in these traits. If a characteristic is only due to the environment there should be no difference

• Ethology: study of animal behaviour in the natural environment
• Tinbergen & Lorenz believed that many species-specific social reactions are based on: genetically pre-programmed fixed-action patterns and triggered by genetically pre-programmed releasing stimuli
• Fixed-action patterns: herring gull chick beak-pecking. Gull herring chicks peck at red spot on adults' beak. This induces the adult gull herrings to regurgiate food. Chicks instinctively know how to do this from when they hatch
• Imprinting: newborn ducks and goslings follow their mother wherever she goes. They do this from the moment of hatching, suggesting this behaviour is genetically inherited. Lorenz stated there was a 12-17 hour critical period after hatching where goslings imprinted.