Lecture Notes - 5 - May 30th

7/29/2019 Lecture Notes - 5 - May 30th

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Chapter 4

NATURE AND

NURTURE


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NATURE AND NURTURE

How did Stephanie Germanotta become Lady Gaga?Was she born this way?


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NATURE AND NURTURE

Behavior Geneticists study our diferences and weigh the relative efects ofheredity and environment.


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GENES: OUR CODES FOR LIFE

The nucleus of every cell in the bodycontains chromosomes, longthreadlikemolecules made up of two twistedstrands of DNA.

D N A carr ies a l l the b i o c h e m i c a linstructions involved in the formation

and functioning of an organism.These instructions are packaged in genes -sections of chromosomes that are thebasic

unit of heredity in all living things.

Genes code forproteins, which become thebuilding blocks of cells or help to regulate

a cells functioning.

Chromosomes and GenesThebasic structural unit of all life is the cell, andwithin each cell are chromosomesthat contain our genes.


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The Human Genome

Humans have 46 chromosomes in the nucleus ofeach cell (except for the gametes, which have 23).

These 46 chromosomes are actually 23 pairs, onefrom the father and one from the mother, 22 being non-sex chromosomes and 1 being the sex chromosomes.

The 22 non-sex chromosome pairs are roughly thesame size and shape and carry corresponding genes.

The 1 pair of sex-chromosomes are identical infemales (two x chromosomes) but differ in males (one xchromosome and one y chromosome).

All female eggs have one x chromosome whereasmale sperm either have an x or a y chromosome;hence, males determine sex of baby!

The genome contains the complete set of instructions for making an organism,containing all the genes in that organism.

GENES: OUR CODES FOR LIFE


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NATURE AND NURTURE

How do behavior geneticists tease apart genetic and environmental influences ondevelopment?

Gene and Environment Influences

Behavior geneticists use twin and adoption studies to look at the relative contributions ofour genes and the environment to various human characteristics.


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NATURE AND NURTURE


Twin Studies

1. Identical vs. Fraternal Twins

Identical twins develop from a single fertilizedegg that splits in two. They are geneticallyidentical, sharing 100% of their genes.

Fraternal twins develop from separate fertilizedeggs and, like regular siblings, share only 50% of

their genes.


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NATURE AND NURTURE


Twin Studies


By measuring pairs of identical and fraternal twins reared in the sameenvironment(so holding environmental influences constant), you can look at how genesinfluence some characteristic.

Identical(monozygotic)TwinsSame Rearing Environment

Fraternal(dizygotic)TwinsSame Rearing Environment

How similar are the twin pairs on some personality characteristic?


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NATURE AND NURTURE


Twin Studies



r = .86 .60


Fraternal(dizygotic)TwinsSame Rearing Environment

>

Given same rearing conditions (same environmental influences), the higher correlation

for identical twins over fraternal twins reflects genetic influences.

r =


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NATURE AND NURTURE


Twin Studies



So what have we learned from these studies?

The personalities of identical twins are much more similarthan fraternal twins.

Studies of thousands of twin pairs in Sweden, Finland, and Australia, for example, find that on both

extraversion(outgoingness) and neuroticism(emotional instability), identical twins aremuch more similar than fraternal twins.

And what does this tell us?

This tells us that our personalities are shaped to some extent by our genes.


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NATURE AND NURTURE


Twin Studies

2. Identical vs. Identical Twins

Bymeasuring pairs of identical twins reared in the same environment and pairs ofidentical twins reared in different environments, you can look at how theenvironment influences some characteristic.


Identical(monozygotic)TwinsDiferent Rearing Environment

Again, how similar are the twin pairs on some personality characteristic?


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NATURE AND NURTURE


Twin Studies

r = .86 .72


Identical(monozygotic)TwinsDiferent Rearing Environment



>Given diferent rearing conditions (diferent environmental influences), the diferent

correlation for the two groups of identical twins reflects environmental influences.


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NATURE AND NURTURE


Twin Studies



So what have we learned from these studies?

The personalities of identical twins reared apart are somewhat less similar than thepersonalities of identical twins reared together.

And what does this tell us?This tells us that nonshared environment (experiences unique to each individual)increases thediferences among individuals.


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NATURE AND NURTURE


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NATURE AND NURTURE

How exactly do diferent experiences make twins diferent?

As it turns out, these experiences(different diets, drugs, stressors, etc) canaffect epigenetic molecules (methyl molecules) that alter geneexpression.

Rats, licking and Stress Response

Infant rats deprived of their mothers normal licking expressrelativelyfew glucocorticoid receptors (the genes are shut down bymethyl molecules) and go on to deal with stress more poorly(because sympathetic arousal is not being turned off).

http://learn.genetics.utah.edu/content/epigenetics/rats/


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NATURE AND NURTURE


Adoption Studies

Bymeasuring biological parent, adoptive parent, and adopted child, you can lookat whether genes orthe environment is a more important determinate of somecharacteristic.

Biological Parents Adoptive Parents

Child

How similar is the child to the biological and adoptive parents on some personalitycharacteristic?


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NATURE AND NURTURE


Adoption Studies

r = .24

Biological Parents Adoptive Parents

Child

r = .01


The higher correlation for children with their biological parents than with their adoptive

parents reflects genetic influences.

>


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NATURE AND NURTURE


Adoption Studies


Why doesnt shared environment make siblings more similar?

Some reasons include: 1) diferent parental treatment, 2) diferent peers, 3) diferentsibling interactions.

Does parenting matter then?

Studies suggest that peer influence is an important kind of nonshared personality influence.Perhaps because of the pressure to fit in,children often conform to the norms and rulesof their peer groups (kids with peers low in conscientiousness often become likewise). Parents,however, to some extent influence who their children become friends with.

Also, even if parents have little influence over their childrens developing personalities, parents doinfluence their childrensattitudes, values, manners, faith, and politics.


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NATURE AND NURTURE

Temperament and Heredity

Temperament refers to a constitutionally based disposition to respond to theenvironment in certain ways.

Inhibited - High Reactivity Uninhibited - Low Reactivity

Fearful Anxious

Withdrawn

Mild stress results in elevated heart rates,brain activity, and stress hormones

Bold Relaxed

Outgoing

Mild stress does not trigger elevated heartrates, brain activity, or stress hormones

Jerome kagan- Inhibited and Uninhibited Temperaments

How is temperament measured?

Jerome Kagan has focused his research ontwo kinds of extreme temperament styles:inhibited anduninhibited.


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NATURE AND NURTURE



How stable is temperament over time?

Temperament has been shown to exhibit remarkable stability. Childrenthat are behaviorally(un)inhibited when infants are usuallybehaviorally (un)inhibited when older (though, itshould be noted, not all inhibited children become inhibited adults)


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NATURE AND NURTURE



How stable is temperament over time?

Temperament has been shown to exhibit remarkable stability. Childrenthat are behaviorally(un)inhibited when infants are usuallybehaviorally (un)inhibited when older (though, itshould be noted, not all inhibited children become inhibited adults)


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GENETIC INFLUENCES ON PERSONALITY

Website: http://www.thepowerofintroverts.com

Susan Cain

http://www.youtube.com/watch?v=c0KYU2j0TM4

This is not examinable. But if youre interested in understandingintroversion (whether your own or that of others), a nice starting place:


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NATURE AND NURTURE

Genes and Environment Influences

1. These genetic studies suggest, then, that our genes set the stage for our personalities,pushing us to develop one way over another (e.g., someone with a very reactive nervous

system will likely end up quite introverted, but thats not to say they cant to some extent learn tobecome more relaxed in social gatherings).

2. Critically, however, the personality characteristics that are ultimately expressed verymuch depend on the interaction between a persons genetic makeup and theirenvironment(e.g., epigenetic influences; see next two slides for other illustrations).

So what might we conclude from these genetic studies?


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NATURE AND NURTURE

Infants with PKU(cause by a recessivegene on chromosome 12) cannot

m e t a b o l i z e the amino acidphenylalanine.

Over time it will build up and maylead to mental retardation.

If identified early, and the infant isplaced on a strict diet free of

p h e n y l a l a n i n e, the infant willdevelop normally.

Genetic - Environment Interaction: Phenylketonuria(PKU)

So the same genotype may develop very diferently depending on how environmentalfactorsinteract withthose genes.


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Genetic - Environment Interaction: Abusive Parenting and Antisocial Behavior

MAOA i s a s e x- l i n k e d g e n e (found on Xchromosome) that is known to inhibit brain

chemicals associated with aggression.Looked at children that had a relatively inactive formof the gene and those with the normal form of thegene.

Found 85% of those that were maltreated ANDthat possessed the relatively inactive form of

MAOA developed some form of antisocialbehavior, and they were 10 times more likely to beconvicted of a violent crime (Caspi et al, 2002).

So simply having the relatively inactive form of the gene is not sufficient for thedevelopment of antisocial behavior; it also requires abusive parenting.

GENETIC INFLUENCES ON PERSONALITY


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NATURE AND NURTURE

How did Stephanie Germanotta become Lady Gaga?Was she born this way?

Stephanie Germanotta was born with a genotype that had the potential to express itselfin a particular way, and she just happened to have those experiences (epigenetic influencesand gene-environment interactions)that led to that genotype expressing itself as Lady Gaga!


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QUESTION #5

After genetic tests on your new baby boy, you are told that he may experience somedevelopmental difficulties. Inquiring further, you learn that there is some concern that asyour child grows up he may be prone to antisocial behavior.

Given this information, answer the following questions. What genetic anomaly(discussed in

lecture) might suggest your child could become antisocial? Does this finding all but consignyour child to a troubled social life? What can you do, if anything, to help your child to developnormally? Finally, comment on how this situation speaks to how nature and nurture interactto affect development. In answering this question be sure to draw an analogy between yoursituation and relevant research (i.e., just like some study found such and such, I would expectthat if I too did such and such that I would observe the same outcome).

This question(as with all questions) is to be answered in a maximum of one page, double-spaced,

using 12 point, Arial font.

Lecture Notes - 5 - May 30th

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