Genes and Behaviour Introduction PDF

Introduction 02 October 2023 10:38 Main Ideas Individual differences Nature & Nurture Heritability Twin & Adoption studies ACE model Assortative Mating Notes Species universals --> group differences --> variability CAN separate nurture & nature Focusing on population statistic rather than individual...

Introduction 02 October 2023 10:38 Main Ideas Individual differences Nature & Nurture Heritability Twin & Adoption studies ACE model Assortative Mating Notes Species universals --> group differences --> variability CAN separate nurture & nature Focusing on population statistic rather than individual Extent to which genetic/environmental factors influence individual differences Differences in average between groups might not be related to individual differences Twin studies = MZ twins vs DZ twins Adoption studies = non-adoptive vs adoptive (i.e., shared genes vs shared environment) Twin Design - comparison between similarity/differences of identical vs non-identical ○ If genetic factors important MZ twins would be more similar ACE model - Additive genetics - Common (Shared) Environment - Environment specific to each twin (non-shared environment) Additive genetics --> individual differences caused by the independent effects of alleles or loci that add up nonadditive genetic variance (e.g. Dominance), in which the effects of alleles or loci do not simply ‘add up’ ○ Genetic influence (A) indicated when r identical twins > r fraternal twins ○ The greater resemblance would be expected based on MZ twins sharing all their polymorphic genes ○ Dominant genetic facts = MZ > 2DZ Common environment ○ Shared environmental influence (C) = non-identical twins more similar than expected by genetic relatedness Environment specific --> Environmental influences that contribute to differences between family members ○ Non-shared environmental influence (E) = identical twins not 100% identical Any trait that can be reliably and separately measured for individuals of different degree of relatedness (e.g. MZ and DZ twins) can be studied within behavioural genetic framework Vp = A + C + E ○ Vp = variance on any phenotype ○ allow us to decompose the phenotypic variance (Vp) to its genetic (A), shared environmental (C) and non-shared environmental components (E) Assumptions of twin methods ○ Genetic correlation between MZ twins is 1.0 ▪ Exceptions due to: skewed X-inactivation, epigenetics ○ Equal Environments Assumption ▪ Environmental variance with MZ and DZ twin pairs will be the same with respect to the environments that influence the behaviour/trait under study ▪ This assumption tested by comparing trait similarity by “real” and “perceived” zygosity ○ Differences between MZ and DZ twins in sharing amniotic sac or placenta do not account for differences in the phenotype of interest ▪ Studies found that have this has little differences ○ Findings from twins generalise to singletons ▪ Twins more likely to be born prematurely, have lower birth ▪ rate have slower language development ▪ Experience more adverse intrauterine environments ▪ twins are similar to non-twins on most traits and twin studies routinely exclude individuals with medical complications from analyses Research suggests that assortative mating does occur + tends to be positive (people with similar traits/attributes gravitate together) ○ assortative mating, in human genetics, a form of nonrandom mating in which pair bonds are established on the basis of phenotype (observable characteristics). ○ For example, a person may choose a mate according to religious, cultural, or ethnic preferences, professional interests, or physical traits ○ To the extent that a trait is under genetic influence, positive assortative mating reduces genetic variation & makes DZ twins more similar to one another - increasing C and decreasing A Assumptions of adoption design: ○ Families involved in the adoption process are representative of the population ○ Biological parents’ contribution is limited to genes ○ Selective placement does not invalidate the conclusions of adoption studies ○ Genetic = Biological Relatives + Environmental = Adoptive Relatives Differences between bio parents, adoptive parents and adopted children ○ Are they representative of the general population> For example, adoptive parents tend to be older Prenatal environment: ○ It is assumed that adopted children are only similar to their birth mothers because of shared genes ○ IVF studies provide a method for disentangling the prenatal environment from genetic relatedness Selective placement: ○ If biological and adoptive parents are matched then the validity of adoption studies may be questioned ▪ For instance, children may be similar to their biological parents for environmental reasons as well as genetic reason ▪ However, little evidence of selective placement Summary Twin and adoption studies can be used to investigate the relative importance of genetic and environmental influences in drivi ng individual differences Twin studies common, adoption studies less common If data from twin and adoption studies are in agreement, this provides stronger evidence than either method alone PSYC0036 Genes and Behaviour Page 1