Genetics and Behaviour Flashcards
What are the three sub-headings under genetics and behaviour?
Genes and Behaviour, Genetic Similarity and Evolutionary explanations for behaviour
What studies support the role of genes in behaviour?
Caspi, Kobiella and (Beck)
What studies support the evolutionary explanations for behaviour?
Brown and Kulik, Sharot et al, Buss
Kobiella et al
Investigated whether variants of the 5HTT gene affect amygdala reactivity by acting on serotonin transporter levels or by influencing the brains development. Kobiella determined the allele combinations for allocation of groups ( and found the combinations to be S and S, S and L and L and L combinations). Then used fMRI scans to measure the reactivity of amygdala to emotionally pleasant, unpleasant and neutral photos, MRI scans to determine the volume of their amygdalae and PET scans to measure the avaliability of the 5HTT ( the serotonin transporter protein).
5HTT was associated with the activation of the left amygdala in response to unpleasant stimuli with the S allele having stronger responses
Caspi et al
C=Calender
Investigated whether variants in the 5HTT gene moderate psychopathological responses to stressful situations. Determined the allele combination of all participants ( S/S, S/L/ L/L) and used a caldender to identify occurence of certain stressful life events and a diagnostic interview schedule as a measure of symptoms in the past year of depression.
Stressful life events increase the likelihood of experiencing depression with the L/L combination being the most protected and the S/S combination being less.
These analyses attest that the 5-HTT gene interacts with life events to predict depression symptoms, an increase in symptoms, depression diagnoses, new-onset diagnoses, suicidality, and an informant’s report of depressed behavior.
What are genes?
A sequence of DNA. They have an effect on behaviour through gene expression – the sending of signals from the gene to outside the cell.
Sharot et al
The aim of this study is to explore the neutral basis of flashbulb memories and to clarify the characteristics of the emotional events that may give rise to them. The participants, ppts, were placed in a fMRI scanner and then asked to retrieve autobiographical memories from cue words presented on screen. The memories were either to be from an event from the summer of 2001 or from 9/11(“September”, then the ppts were asked to rate them on arousal, vividness, reliving, remember/ know, confidence and valence. Finally, ppts were asked to write a description of the two memories that had been recalling during the study. They found that the downtown group’s memories (closer to the event) elicited stronger emotions, were more vivid, were more frequently re-lived and were more clearly and confidently remembered than for the Midtown group. They also found that the closer ppts were to the Twin Towers on 9/11, the bigger the difference between the 2 accounts so this concludes that the closer to the event, the more direct personal experiences.
Kendler et al
To determine the genetic and environmental contributions to depression in a large cohort of twins. Twins from the registry were contacted by telephone across a period of five years.
Each was interviewed to determine:
Possible depression during previous twelve months (using standardised interview form);
Zygosity (whether the twins were identical or not) which was self-reported not biologically determined and biographical details
-Concordance rates( the likelihood of a person developing a condition if their twin develops it)
weren’t related to how long the twins had lived together in their “home of origin”.
-Concordance rates were higher for identical (monozygotic) twins than for non-identical (dizygotic) twins.
Concordance rates were higher for female-female sets of twins than for male-male sets.
Heritability of MDD across all ppts, once extraneous variables were controlled for, was about 38% (matches average - 37% - of many other studies).
Heritability for women was estimated at 42%, and at 29% for men (close to other studies’ averages of 40% and 31% respectively).
The contributions of genetic and environmental factors remained stable across different generations, despite significant social change across that time.
-As concordance rates weren’t affected by time spent together in childhood, but were affected by whether twins were identical (100% shared genes) or non-identical (c.50% shared genes), this points to a genetic component to depression.
-The higher concordance rates for same-sex female sets of twins suggests that genes for sex might interact with genes related to depression.
They suggest this might be hormone-related: women experience more hormonal fluctuations (and higher levels of some hormones) that might affect the way the genes influence depression.
-They didn’t include a consideration that being female might expose an individual to more sociocultural stressors than if they were male (weakness?).
What is a twin study?
studying twins raised in the same family environments, which provides control not only for genetic background but also for shared environment in early life.
As monozygotic (identical) twins develop from a single egg fertilized by a single sperm, which splits after the egg starts to develop, they are expected to share all of their genes, whereas dizygotic (fraternal) twins share only about 50% of them, which is the same as non-twin siblings.
Thus, if any excess similarity is seen between the identical twins when a researcher compares the similarity between sets of identical twins to the similarity between sets of fraternal twins for a trait or condition, then most probably the reason behind this similarity is due to genes rather than environment.
