Behavioral Genetics
Comportemental geneistry is a domain of scientific research which uses genetic methods to examine the nature and origins of individual behavioral differences. Although the word “competent genetics” focuses on genetic factors, mental and environmental factors are examined widely using research designs to remove the confusion.
Conducting genetic study findings have largely affected contemporary knowledge of the role of genetic and environmental effects on behaviour. These include the proof that almost all investigated behaviour, which tends to improve as people become adults, are under important genetic impact. Moreover, a very big amount of genes influence most studied human behaviours, with very tiny individual effects of these genes. There is also a powerful position in environmental factors, but they tend to differentiate family members, not more comparable.
Behavioral Genetics Comportemental geneistry domain scientific genetic methods examine nature origins individual behavioral differences Although word competent genetics focuses genetic factors mental environmental factors examined designs remove confusion Conducting genetic study findings contemporary knowledge role genetic environmental effects behaviour These include proof investigated behaviour improve people adults genetic impact Moreover big genes influence studied human behaviours tiny individual effects genes There powerful position environmental factors tend differentiate family members comparable Behavioural genetics referred behaviour genetics field scientific genetic methods investigate nature origins individual differences behaviour While behavioural genetics connotes focus genetic influences field broadly investigates genetic environmental influences designs removal confounding genes environment Behavioural genetics founded scientific discipline Francis Galton late 19th century discredited association eugenics movements World War 20th century field renewed prominence inheritance behaviour mental illness humans typically twin family studies genetically informative model organismsthrough selective breeding crosses late 20th early 21st centuries technological advances molecular genetics measure modify genome This led major advances model organism knockout mice human studies genome wide association studies leading scientific discoveries Findings behavioural genetic broadly impacted modern understanding role genetic environmental influences behaviour These include evidence researched behaviors degree genetic influence influence increase individuals develop adulthood Further researched human behaviours influenced large number genes individual effects genes small Environmental influences play strong role tend family members HistoryFarmers wheat cattle Ancient Egyptian art BCE displaying domesticated animals Selective breeding domestication animals earliest evidence humans considered idea individual differences behaviour natural Plato Aristotle speculated basis mechanisms inheritance behavioural characteristics Plato argued The Republic selective breeding citizenry encourage development traits discourage today called eugenics encouraged pursuit ideal society Behavioural genetic concepts existed English renaissance William Shakespeare coined terms nature nurture The Tempest wrote Act Scene Caliban devil born devil nature Nurture stick Modern day behavioural genetics began Sir Francis Galton nineteenth century intellectual cousin Charles Darwin Galton polymath studied subjects including heritability human abilities mental characteristics One Galton investigations involved large pedigree study social intellectual achievement English upper class 1869 years Darwin Origin Species Galton published Hereditary Genius work Galton rate eminence highest close relatives eminent individuals decreased degree relationship eminent individuals decreased While Galton rule role environmental influences eminence fact acknowledged study served initiate debate relative roles genes environment behavioural characteristics Through work Galton introduced multivariate analysis paved modern Bayesian statistics sciences launching dubbed Statistical Enlightenment Galton yearsThe field behavioural genetics founded Galton ultimately undermined Galton intellectual contributions founding eugenics movement 20th century society The primary idea eugenics selective breeding combined knowledge inheritance behaviour improve human species The eugenics movement subsequently discredited scientific corruption genocidal actions Nazi Germany Behavioural genetics discredited association eugenics The field gained status distinct scientific discipline publication early texts behavioural genetics Calvin Hall 1951 book chapter behavioural genetics introduced term psychogenetics enjoyed limited popularity 1960s 1970s However eventually disappeared usage favour behaviour genetics The start behavior genetics identified field marked publication 1960 book Behavior Genetics John Fuller William Robert Bob Thompson accepted behaviours animals humans genetic influence extent genetic influence trait differ decade February 1970 issue journal Behavior Genetics published 1972 Behavior Genetics Association formed Theodosius Dobzhansky elected association president The field grown diversified touching scientific disciplines MethodsThe primary goal behavioural genetics investigate nature origins individual differences behaviour wide variety methodological approaches behavioral genetic outlined Animal studiesAnimal behavior genetic studies considered reliable studies humans animal experiments variables manipulated laboratory animal selection experiments employed For laboratory house mice bred open field behaviour thermoregulatory nesting voluntary wheel running behaviour range methods designs covered Behavioural geneticists model organisms employ range molecular techniques alter insert delete genes These techniques include knockouts floxing gene knockdown genome editing methods CRISPR Cas9 These techniques behavioural geneticists levels control model organism genome evaluate molecular physiological behavioural outcome genetic Animals commonly model organisms behavioral genetics include mice zebra fish nematode species elegans Twin family studiesPedigree chart showing inheritance pattern consistent autosomal dominanttransmission Behavioural geneticists pedigree studies investigate genetic environmental basis behaviour Some designs behavioural genetic variations family designs pedigree designs including twin studies adoption studies Quantitative genetic modelling individuals genetic relationships parent child sibling dizygotic monozygotic twins estimate extent genes environment contribute phenotypic differences individuals The basic intuition twin study monozygotic twins share genome dizygotic twins share average segregating genome Thus differences members monozygotic twin pair differences environment dizygotic twins differ environment genes Under simplistic model dizygotic twins differ monozygotic twins attributable genetic influences assumption twin model equal environment assumption monozygotic twins shared environmental experiences dizygotic twins monozygotic twins tend experiences dizygotic twins experiences genetically mediated gene environment correlation mechanisms monozygotic twins tend dizygotic twins reasons genes Measured genetic variantsThe Human Genome Project allowed scientists genotype sequence human DNA nucleotides Once genotyped genetic variants tested association behavioural phenotype mental disorder cognitive ability personality Candidate Genes One popular approach test association candidate genes behavioural phenotypes candidate gene selected based priori theory biological mechanisms involved manifestation behavioural trait phenotype general studies proven difficult broadly replicate concern raised false positive rate type high Genome wide association studies genome wide association studies researchers test relationship millions genetic polymorphisms behavioural phenotypes genome This approach genetic association studies atheoretical typically guided biological hypothesis phenotype Genetic association findings behavioural traits psychiatric disorders highly polygenic involving small genetic effects SNP heritability heritability Recently researchers begun similarity classically unrelated people measured single nucleotide polymorphisms SNPs estimate genetic variation covariation tagged SNPs mixed effects models implemented software Genome wide complex trait analysis GCTA researchers average genetic relatedness SNPs individuals typically large sample Haseman Elston regression restricted maximum likelihood estimate genetic variation tagged predicted SNPs The proportion phenotypic variation accounted genetic relatedness called SNP heritability Intuitively SNP heritability increases degree phenotypic similarity predicted genetic similarity measured SNPs expected true narrow sense heritability degree measured SNPs fail tag typically rare causal variants The method independent estimate heritability require assumptions twin family studies insight allelic frequency spectrum causal variants underlying trait variation Quasi experimental designsSome behavioural genetic designs understand genetic influences behaviour control genetic influences test environmentally mediated influences behaviour Such behavioural genetic designs considered subset natural experiments quasi experiments attempt advantage naturally occurring situations mimic true experiments providing control independent variable Natural experiments experiments infeasible practical ethical limitations general limitation observational studies relative influences genes environment confounded simple demonstration fact measures environmental influence heritable Thus observing correlation environmental risk factor health outcome evidence environmental influence health outcome Similarly observational studies parent child behavioural transmission impossible transmission genetic environmental influences problem passive gene environment correlation The simple observation children parents drugs drugs adults children drugs grow children modelling parents behaviour Equally plausible children inherited drug predisposing genes parent increased risk drug adults parents behaviour Adoption studies parse relative effects rearing environment genetic inheritance small negligible rearing environment smoking alcohol marijuana children larger rearing environment harder drug Other behavioural genetic designs include discordant twin studies children twins designs Mendelian randomization General findingsThere broad conclusions drawn behavioural genetic nature origins behaviour Three major conclusions include behavioural traits disorders influenced genes environmental influences tend members family influence genes increase relative individuals age Genetic influences behaviour pervasiveIt clear multiple lines evidence researched behavioural traits disorders influenced genes heritable The single largest source evidence twin studies routinely observed monozygotic identical twinsare sex dizygotic fraternal twins The conclusion genetic influences pervasive observed designs depend assumptions twin method Adoption studies adoptees routinely biological relatives adoptive relatives wide variety traits disorders Minnesota Study Twins Reared Apart monozygotic twins separated shortly birth reunited adulthood These reared twins twins reared wide range measures including general cognitive ability personality religious attitudes vocational interests Approaches genome wide genotyping allowed researchers measure genetic relatedness individuals estimate heritability based millions genetic variants Methods exist test extent genetic similarity aka relatedness nominally unrelated individuals individuals close distant relatives phenotypic similarity Such methods rely assumptions twin adoption studies routinely evidence heritability behavioural traits disorders Nature environmental influenceJust researched human behavioural phenotypes influenced genes heritable phenotypes influenced environment The basic fact monozygotic twins genetically identical perfectly concordant psychiatric disorder perfectly correlated behavioural traits environment shapes human behaviour The nature environmental influence individuals family Similarity twins adoptees small role shared environment personality Nature genetic influenceGenetic effects human behavioural outcomes multiple ways One terms variance behaviour accounted alleles genetic variant coefficient determination displaystyle intuitive displaystyle describes extent genetic variant individuals harbour alleles behavioural outcome complementary effects individual genetic variants change expects behavioural outcome change number risk alleles individual harbours denoted Greek letter displaystyle beta denoting slope regression equation case binary disease outcomes odds ratio displaystyle disease allele status Note difference displaystyle describes population level alleles genetic variant displaystyle beta displaystyle risk allele individual harbours relative individual harbour risk allele When displaystyle metric effects individual genetic variants complex human behavioural traits disorders vanishingly small variant accounting displaystyle variation phenotype This fact discovered genome wide association studies complex behavioural phenotypes including substance personality fertility schizophrenia depression endophenotypes including brain structure function There small handful replicated robustly studied exceptions rule including APOE Alzheimer disease CHRNA5 smoking behaviour ALDH2 individuals East Asian ancestry alcohol hand assessing effects displaystyle beta metric large number genetic variants large effects complex behavioural phenotypes The risk alleles variants exceedingly rare large behavioural effects impact small number individuals Thus assessed population level displaystyle metric account small differences risk individuals population Examples include variants APP result familial forms severe early onset Alzheimer disease affect individuals Compare risk alleles APOE pose smaller risk compared APP common affect greater proportion population Finally classical behavioural disorders genetically simple etiology Huntington disease Huntington caused single autosomal dominant variant HTT gene variant accounts differences individuals risk developing disease assuming live long case genetically simple rare diseases Huntington variant displaystyle displaystyle simultaneously large Additional general findingsIn response general concerns replicability psychological behavioral geneticists Robert Plomin John DeFries Valerie Knopik Jenae Neiderhiser published review replicated findings behavioral genetics The findings All psychological traits substantial genetic influence traits heritable Heritability caused genes small Phenotypic correlations psychological traits substantial genetic mediation The heritability intelligence increases development Age age stability genetics Most measures environment genetic influence Most associations environmental measures psychological traits mediated genetically Most environmental effects shared children growing family Abnormal normal Behavioral Genetics ZodiacPage
