heritability

Question 1

Heritability is?

Answer 1

measuring (estimating) the extent to which any trait is defined by ‘nature’ or ‘nurture’

Question 2

With regards to nature versus nurture, what is nature?

Answer 2

• Our behaviour is determined by our genes

* Personality traits, abilities, and so on are predetermined at conception

Question 3

What is nurture?

Answer 3

Our behaviour is determined by our upbringing

• Personality traits, abilities, and so on are shaped by our environment and life experiences after conception

Question 4

Explain the genetic basis for behaviour?

Answer 4

That different breeds of dog have different ‘personalities’ is evidence for genetic control of behavior
• Environmental effects on behavior (dogs) > in any breed, environment, experience and training can also influence behavior

Question 5

What makes us, us?

Answer 5

• Genotype and environment INFLUENCE our phenotype (physical apperance and makeup)
  
  • Genotype = the genetic code of an individual – determined at fertilisation of egg
  • Phenotype = the observable outcome, or form, of an individual as determined by genetic and environmental influences ( appearance, development, behavior, personality, intelligence)

Question 6

Identical twins share?

Answer 6

The same genotype but not necessarily the same phenotype
• Similar phenotypes do NOT necessarily indicate shared genotype
• Fingerprints is good for this example

Question 7

Dogs can distinguish odours of identical twins who live apart but?

Answer 7

• BUT NOT identical twins who live in the same house and eat the same food

Even clones would have different fingerprints and body odour!

Question 8

What is heritability??

Answer 8

• The proportion of shared variation in phenotype within a population that is explained by shared genotype
  
  • INDIVIDUAL VARIATION IN THESE TRAITS
  • IT IS NOT EXPLAINING THE EXTENT TO WHICH GENES PLAY A ROLE IN UNIVERSAL/SPECIES TYPICAL TRAITS
  • CAN NOT USE HERITABILITY WHEN WE THINK ABOUT GENETIC INFLUENCE ON INDIVIDUAL’S TRAITS < WE ARE NOT LOOKING AT A GIVEN INDIVIDUAL ( we are looking at individual variation across individuals in a given trait)

Question 9

in what two ways do families offer evidence for genetic effects, and what is the problem with such evidence?

Answer 9

Sir francis galton noted ‘eminence’ ran in families
• Galton coined the term “nature versus nurture”
• Galton found that the correlation between parent’s and children’s IQ around +.45 (significant and moderate correlation which suggests a heritable component to intelligence)
• Problem > parents and children also share the same environment

Lifetime stability of traits
• Traits evident across life might indicate genetic influence
• Ian deary – childhood IQ predicts adult IQ, also mortality
• Childhood personality predicts adult personality ( esp. Mood stability and conscientiousness)

Families and consistency:
• But environments are also stable (including parental behavior)
• Family studies only take us so far

Question 10

Monozygotic and dizygotic have what percent of genes in common?

Answer 10

Mono- 100%

Di- 50%

Question 11

How to determine influence of environment and genes?

Answer 11

• Compare a) identical twins (MZ) and B) non identical (DZ) twins. 100% vs 50% similar genes < higher R for A than B = INDICATES HERITABILITY
• Compare twins reared C) together and d) apart < lower R for D than C indicates = environmental effects
• Compare parents and their e) non-adopted and f) adopted children < 50% vs 0% similar genes
Higher R for e than f indicates HERITABILITY

Question 12

How to calculate heritability?

Answer 12

FALCONERS FORMULA:
• Heritability (H2) = 2 x (Rmz – Rdz)
• H2 tells us about population-level estimates

Question 13

Heritability of personality?

Answer 13

• Estimates vary across studies

* Studies suggests strong personality heratibility and low environmental contribution

Question 14

How might genes affect personality?

Answer 14

• Eg > anxiety is related to low serotonin levels. Drugs that increase serotoning (by blocking its breakdown) decrease anxiety.
  
  • In humans, a serotonin transporter gene (regulates serotoning uptake) accounts for 7-9% of the inherited variation of anxiety-related personality traits

Question 15

Heritability of intelligence?

Answer 15

• Roughly about 50% genetic and 50% environmental
  
  • Results of adoption studies show that environment appears to influence IQ much more than it does for personality
  • One example/indication of environmental influence on IQ = iq scores of deprived children who are fostered to relatively wealthy non-deprived homes changes and increases
  • Environment appears to influence IQ more than for personality
  • Influence of living in a different family can REDUCE THE IQ CORRELATION
  • ADOPTION STUDIES: child & adoptive parent (IQ) = 0.17 whereas for personality, child and adoptive parent = 0.05 ( indicates the environment that the adoptive parent offers is having a much stronger effect in terms of intelligence)
  • Effects of environment can change IQ scores relatively more than personality

Question 16

Almost anything may affect IQ scores, but especially >

Answer 16

• Biological / maternal factors ( nutrition, lead, prenatal conditions)
  
  • Family environment ( birth order, family size, socioeconomic status)
  • School and education
  • Cultural effects ( eg: decontextualization – ability to think abstractly and then generalize)

Question 17

Take home messages?

Answer 17

• Both personality and intelligence show relatively high heritability but personality is relatively UNAFFECTED BY ENVIRONMENT whereas INTELLIGENCE is much more so.

Question 18

It is increasingly recognised that there are several issues with twin studies, and to a lesser extent with adopted family studies, explain?

Answer 18

1) They are not representative of the general population… the families are somewhat unusual (e.g. they are often larger)
2) Twin studies may overestimate genetic effects, because MS twins share more common environments than DZ twins, and have more similar social experience
3) There are important difference between shared (e.g. same house, parents) and non-shared (friends, relationships) environments. The non-shared experience may be especially influential. The degree of difference in non-shared environment predicts differences in adult personalities between siblings.
4) Adoptee studies may overestimate environmental effects, because agencies select adoptive families carefully (e.g. for sufficient wealth)

Question 19

Prenatal environmental effects?

Answer 19

Recall that differences in the uterine environment can lead to masculinisation in female mice who are exposed to testosterone from neighbouring male siblings?
Similar effects occur in humans: Prenatal testosterone is linked to long-term effects in females who share womb with male twin. (Links to an external site.)Clearly this has implications for interpreting DZ twin correlations.

Question 20

Epigenetic effects?

Answer 20

Finally, the importance of epigenetic effects is increasingly recognised, which certainly have potential to alter conclusions of straightforward heritability studies. Epigenetics relates to heritable changes not in gene inheritance but in gene expression, such as whether genes are turned on or off. There are nice examples of this in the final article below, on free will, ranging from cherry-fearful mice offspring to upregulated stress hormones in children of Holocaust survivors.
But my favourite is the study of survivors and descendents of a late 19th century famine in Överkalix, Sweden. It’s interesting because it describes 2 interesting effects:
• grandchildren of survivors who had a relatively good food supply have lower risk of cardiovascular disease, compared to those whose grandparents survived but suffered more. This is an epigenetic effect.
But also:
• For men born or growing up in the famine: their grandsons (but not grand-daughters) had elevated risk
• For women born or growing up in the famine: their grand-daughters (but not grandsons) had elevated risk
• These effects are only transmitted through paternal grandparents, not maternal grandparents
These are male-line parent-of-origin epigenetic effects! Mind-blowing. If you’re intrigued, the paper can be found here (Links to an external site.)