Week 7: Genes, Environment, and Development

This is the 7th week of my Behavioral Genetics class, and we are also right in the middle of moving, so this week's notes are even rougher than usual.  Here are things I hope to remember about genes and development:  

Evidence for existence of shared and nonshared effects

 • Schizophrenia – Predominant source of environmental influence appears to be non-shared

 • General Cognitive Ability – Predominant source of environmental influence appears to be shared 

• In general – Predominant source of environmental influence appears to be non-shared 

There are, however, some behavioral traits that show a shared environmental effect (this might be because these are the domains that parents focus on when they rear):

• General cognitive ability 

• Antisocial and rule-breaking behavior 

• Social attitudes including religiousness

Liberal v. conservative:  no heritable effect, all environment - until age 20, then there is suddenly heritability in political leanings.  

(For those traits that show shared environmental influence (e.g., GCA, social attitudes, and rulebreaking) the strength of that influence declines markedly once relatives move apart.)

For general cognitive ability, genetic influence increases with age.  (This is interesting because you would expect it to be the opposite - that environmental influence would increase with age as more life experiences pile up.)  Why is this?  as children grow up, they increasingly select, modify and even create their own experiences in part based on their genetic propensities.

Gene Environment Correlation:  Statistical correlation between the magnitude of genetic effect and the magnitude of environmental effect

3 types of Gene Environment Correlation:

1.  Passive - Parents who transmit genes that promote the development of a specific trait are likely to also create a rearing environment that fosters the development of that trait  (eg high ability)

2.  Reactive - Our experiences are in part a function of the reactions our behaviors elicit from others and to the extent our behavior is genetically influenced, this induces a G-E correlation  (eg, fussy baby elicits a different reaction than a happy baby)

3.  Active - Our experiences are in part a function of the choices we make based upon our abilities and interests. And to the extent our abilities and interests are genetically influenced, this will induce a G-E correlation  (for example, choosing to go to the library and study v. going to the bar to drink)

Parent behavior is related to offspring functioning.  Is this environmentally causal or genetic?

Example:  overprotective parents have anxious kids.  (It's possible that parents are overprotective because they are anxious, and their anxiety was genetically passed down to kids - so not environmentally caused.)  (Also possible that it's reactive - anxiety in the child elicits overprotectiveness in the child.)

Robust association between mother smoking during pregnancy and ADHD.  Is this causal?

- Mothers who smoke may have other things in common with each other, and that other thing is common is actually the thing that increases the risk of ADHD.  

- Effective way to test this is sibship design...in this example, mom smokes during first pregnancy but not second.  You find enough of this circumstance and run the numbers.