Heritability and Genetics Flashcards
twins and adoption studies demonstrate
relative proportion of genetic and environmental influence on personality traits
molecular genetic studies demonstrate
individual genes which influence personality
additive genetic assumption
linear increase in trait similarity as proportion of genes shared by two individuals increases
ways which additive genetics may be incorrect
genetic dominance- dz twins which share 25% wont be 50% less then mz
epistasis- traits from combination of genes
equal environments assumption
similar shared environments of twins
pleiotropy
effect of a gene on two or more phenotypic outcomes
What is DNA comprised of
nucleotide base pairs (A,T,C,G)
what do genes code for and where are its codes regions
code for proteins
exons
what are alleles
specific form of a gene
what is Single nucleotide polymorphisms (SNPs)
type of genetic variation- single base pair on the DNA strand
Genotype
combination of different alternative forms of gene (alleles) possessed by an individual
Phenotype
totality of observable traits and characteristics of an individual
Heritability studies include
Family, Twin and Adoption studies
Family studies
Genetic similarity decreases with distance from index case
Heritability coefficient
proportion of variance attributable to genetic variation
Trait heritability from twin and adoption studies
Bouchard-
personality 40%
Mental ability 20-80%
schizophrenia 80%
major depression 40%
heritability estimates from twin and adoption studies
twin 40%
adoption 30%
limitations of heritablity
shared environments not all equal
twin and adopted children not representative
genes + environment not operating independently
3 main techniques of molecular genetics
Linkage analysis
candidate gene association
Genome-wide association
Linkage analysis
used to study rare phenomenon this is simple and has a large effect size
marker genes used to indicate disease genes
Candidate gene association requirements
hypothesis driven (knowledge needed) and large sample size and homogeneous (to prevent confounds)
Candidate gene association
pick specific allele and compare cases to controls. Measure trait variation across genotype groups
Candidate gene association example
lesch et al - serotonin linked to anxiety. 5HTT modulates. short allele associated with reduced 5HTT and increased anxiety
Against candidate gene association
Munafo et al - initial finding not supported by further studies. suggesting other effects operating
any true effects of single genes likely to be minimal
Genome-wide association requirements
Uses SNPs.
over 300,00 SNPs examined using DNA microarrays.
dose not require an hypothesis
Evidence for genome wide association
Neuroticism- significant association of an SNP involved in bipolar, schizophrenia and depression
Criticism of genome wide association
polygenic- traits shaped by large number of common alleles each having a small effect
large sample sizes required
meta-analysis uses may include difference in personality scales or properties (characteristics)
Gene and environment studies
Caspi et al - 5HTT gene associated with neuroticism and depression
childhood trauma also associated
5HTT gene moderated effect of maltreatment leading to depression
