week 6- persinality: nature and nurture

twin studies

extraversion- 0.53

neuroticism- 0.41

consscienciosness- 0.44

agreeablness - 0.41

openess- 0.61

Twin and family studies

Heritability estimates in the range of 40% are common when resemblances between MZ twins is compared with resemblances between DZ twins (see also Johnson et al., 2008; van den Berg et al., 2014; Polderman et al., 2015; Vukasović and Bratko, 2015).

• Heritability estimates are typically slightly lower (~30%) in family/adoption studies where the resemblance between parent/biological child, or relatives separated by adoption, are compared (e.g. Bouchard and Loehlin, 2001; Rijsdijk and Sham, 2002). • Heritability estimates do not appear to vary by sex (van den Berg et al., 2014; meta-analysis of data from over 29,000 twin pairs).

Candidate genes approach: Extraversion

• Q: Variation in the DRD4 dopamine receptor gene associated with Novelty Seeking (≈ Extraversion)? • It is a polymorphic gene (i.e. it occurs in several forms). This polymorphic region typically includes 2 to 11 repeats - 3 most common variants (DRD4 2R, DRD4 4R, DRD4 7R).

• DRD4 7R results in the expressed dopamine receptor having less affinity for dopamine binding.

• People with at least one 7-repeat allele have higher Novelty Seeking than other genotypes

Dopamine D4 Receptor Gene Variation:

Infidelity and Sexual Promiscuity

Candidate genes approach: Neuroticism & the serotonin transporter gene

Serotonin transporter gene (5 HTT) terminates the action of serotonin by facilitating its reuptake from the synapse.

• 5-HTTLPR: a polymorphism in the promoter region of the 5HTT gene.

• a 44bp deletion/insertion generated two alleles of 5 HTTLPR: Short (14-repeat) and Long (16-repeat).

• The short allele appears to be associated with decreased serotonergic function

Individuals with either one or two copies of the short 5 HTTLPR allele (so Short/Long or Short/Short) had higher Neuroticism scores that individuals homozygous for the long variant (Long/Long).

• Concluded that the 5-HTT polymorphism accounted for 3 4% of total variation (and 7-9% of inherited variance) in anxiety-related personality traits in individuals

The problem of non-replication

By 2003, Munafo et al. identified 79 studies reporting associations between genes and personality traits. • Most report at least one significant result, but results vary.

• Pooling the data, evidence is strongest for HTTLPR, some indications for DRD4.

• However, effects are small – a few percent of variance is explained; may also vary with sex and ethnicity.

• Hence, to reliably detect these associations you need thousands of participants. • Even if they are real, the don’t explain much of the genetic basis of personality.

Genome-Wide Association Studies (GWAS) Approach

Instead of having a candidate gene in mind, you set markers across the whole genome. • Should find all variants associated with phenotype of interest. • Hypothesis-free • Exploratory • Lower power • Large number of variants

GWAS and the problem of the missing heritability

For personality, each GWAS finds some associations, but these initially explain <1% of the variance in personality, and usually did not replicate across studies.

• Problem of the missing heritability: Was described as “one of the great puzzles of current genetic research (Maher, 2008; Manolio et al., 2009)” (De Young and Clark, 2012).

We need to consider the epigenome also!

The Epigenome (Epi = above) is a secondary layer of biochemical information that modify or mark the genome in a way that alters the instructions given by the DNA. • Epigenetic factors, whilst not part of the DNA, impact on DNA and gene activation >> influence which genes are turned on and off at different times and places in the body. • Whilst the genome remains largely static within an individual, the epigenome can be altered by the environment. • Moreover, epigenetic changes can be passed from generation to generation via transgenerational epigenetic inheritance.

polygenicity

influenced by two or more genes

Early experience and personality

Childhood experience could explain variation in personality: Everyone agrees that heritability not 100%. The statement above comes from measuring personality with broad, explicit self-rating scales; may not to be true with more specific or behavioural measures. Belsky, Steinberg, and Draper’s (1991; Belsky 2012) theory of the development of reproductive strategies, also known as “psychosocial acceleration theory”.

The Belsky, Steinberg and Draper Hypothesis (1991)

Individuals differ in sex and relationship behaviours, like fidelity, age at onset of sexual activity, sociosexuality, etc

What if early and promiscuous sexuality were an adaptive response to certain types of early experience?

• Unsupportive care from caregivers in first 5-7 years of life is a cue of harsh ecological conditions.

• Q: Does this cause a fast life history strategy (relative to peers who have experienced supportive care) as an adaptive response, to ensure reproductive fitness in an unpredictable/harsh environment.

>> A harsh development context is predicted to stimulate: • earlier pubertal maturation and initiation of sexual activity,

short-term and unstable pair-bonds, and • limited parental investment as individuals sought to bear more children but not care for them intensively.

Childhood experience and age at first pregnancy

Prospective study of about 3000 women born in 1958. Outcome was age at first pregnancy. Predictors four measures of parental investment/stability in first 7 years of life: being breastfed, longest separation from mum, dad’s role, residential moves. Belsky, Steinberg, Draper hypothesis predicts earlier first pregnancy the more adversities there are

Puberty Prediction: Other findings

Maltreated girls reached pubertal maturity 8 months earlier than nonmaltreated girls (Costello et al., 2007). • Harsh parenting at age 4.5 years predicted earlier menarche and, via this effect, indirectly fostered greater sexual risk-taking in adolescence (Belsky et al., 2007, 2010). • Does not appear to apply to males (James et al., 2012).

causality

Candidate genes are, at least, complete genes. • SNPs are parts of genes, markers, modifiers, etc… • But the basic mechanism of organismal biology requires genes

Fundamentals of “Evo Devo” biology

We have about 20,000 genes that code for proteins. • But there are (currently estimated) between 100,000 and over 1,000,000 unique types of protein. • Alternative splicing • ABCDE ➢ABD ➢ABCE • Post-translational modification • Protein folding • Epigenetics • … and literally all of organismal biology • Devolopment encompasses a lot of things! • Deep homology • Toolkit genes • Internal regulatory networks

Developmental systems theory

All biological processes operate by continually assembling new structures.

• Each such structure transcends the structures that made it. It will have its own systematic characteristics, information, functions and laws.

• Each such structure is nevertheless irreducible to any lower (or higher) level of structure, and can be described and explained only on its own terms.

• The major processes through which life as a whole operates, including evolution, heredity and the development of particular organisms, can only be accounted for by incorporating many more layers of structure and process than the conventional concepts of ‘gene’ and ‘environment’ normally allow for.

• A developmental system can be thought of as similar to “species”. • So we are, each, developmental systems. • Genetic effects are impossible to interpret outside of the developmental system. • Genetics are inseparable from environment

uncovring the complex gentics of human cahrctoristics

used a machine eraning method witch uncoves complec genotypic- phenotypic networks and enviremntal intraction

identifies clusters of SNPs within individuals

“These gene sets modulate specific molecular processes in brain for intentional goal-setting, self-reflection, empathy, and episodic learning and memory.

These appeared consistent across cultures and environments and explained nearly all the heritability expected for character in each sample (50 to 58%). “We postulate that personality heritability is not missing, but is distributed in multiple networks of interacting genetic and environmental variables that influence different people.”

Gean- gean interation GxG

geans intract with each others- have to have geadn a+ and gean B + for it to work the intraction causes teh behvior but if donta hv one aspect of teh egan ther is not behvior

gena- envirement

teh genae and envirent casue the behavior menaing taht if the enviremnt ist presnet it wont cause the beehor