biological - genetics

genome

the totality of your genetic instructions for protein formation contained in your DNA

DNA

made of up nucleotides and joined together through a phosphate group. Each strand of DNA contains thousands of genes

chromosome

made up of strands of DNA coiled tightly around histone proteins

gene

specific sections of DNA that codes for a specific protein. These proteins determine what type of cell a stem cell becomes

twin studies

compare mz with dz twins

adoption studies

compare behaviors of adopted children with different environments. (eg with adoptive parents, biological parents, biological siblings)

family/kinship studies

compare traits/genetic behavior through family generations

molecular genetics

use of modern genetic mapping technology to investigate behavior influence on genes

heritability

statistical measure in % of how much of the variation in a trait is due to variation in genes.

trait

any physical/behavioral expression of a gene

mz twins

develop from 1 fertilized egg which splits to form 2 embryos (share identical DNA)

dz twins

develop from 2 separate fertilized eggs (share 50% DNA)

concordance rate

rate of probability that 2 people with shared genes will develop the same behavior

predisposition

the state of being likely to behave in a particular way or to suffer from a particular disease

niche picking

a phenomenon in which genetic predisposition causes individuals to select certain aspects of the environment resulting in an influence in behavior

gene environment interaction (GxE)

the expression of a certain gene depends on the environmental context

epigenetics

in order for a condition to occur, a gene must be expressed. the gene can still be present and not be expressed and the condition will not occur

diathesis stress model

a psychological theory that attempts to explain behavior as the result of of predispositional genetic vulnerability and stress caused by life experiences

kendler et al

aim: determine the heritability of depression

method: twin study, 15493 complete twins from the national swedish twin registry. only twins with verified zygosity were used

procedure: telephone interviews from March 1998 to January 2003, carried out by a team of trained interviewers. Major depression was assessed using the modified DSM-IV criteria and additionally twins were asked about their individual and specific environment

result: concordance rate of MZ males were 31%, and MZ females were 44%.

The concordance rate of DZ males were 11% and DZ females were 16%

conclusion: depression may be the result of a genetic predisposition

weissman et al

aim: investigate the potential genetic nature of major depression disorder

method: longitudinal kinship study, participants were 161 families with 3 generations

procedure: study took place over 20 years. original sample of depressed patients (now grandparents) was selected from a clinic specialized in treatment of mood disorders. non depressive participants were selected from the same local community. original sample of grandparents (1 gen) and parents (2 gen) were interviewed 4 times. The children (3 gen) were evaluated by clinicians (1 psychiatrist 1 psychologist)

results: high rates of psychiatric disorders in grandchildren with 2 generations showing symptoms of major depression. children had increased risk of any disorder if depression was observed in both grandparents and parents. if a parent was depressed but has no history of depression in grandparents, there was no significant effect of parental depression on grandchildren.

conclusion: psychiatric disorders are more likely to occur in people with a family history of mental illness that goes back 2+ generations

caspi et al

aim: investigate whether a change in the 5HTT gene is linked to risk of depression

method: longitudinal, participants were 1037 children from new zealand

procedure: participants were divided into 3 groups: 1) both short alleles of 5HTT. 2) 1 short 1 long allele of 5HHT. 3) both long alleles of 5HTT. Participants were assessed longitudinally between ages 3-26. a “life of history calendar” was given to asses stressful life events and interviews were conducted to assess symptoms of depression

results: participants with 1 or 2 short alleles of 5HTT reacted to stressful life events with more depressive symptoms

conclusion: the 5HTT gene is responsible for modulating an individuals vulnerability to stress and the predisposition of depression can be linked with stress.