From Last Class...

Single Gene Disorders

• Huntington's
• PKU

Punnett Squares

Chromosome Disorders

• Sex chromosomes
• Down syndrome

Polygenetic Effects

Heritability

• h²

Intelligence

Francis Galton (1822-1911)

• Intelligence
• Twin studies
• Genetic basis

John Stuart Mill (1806-1874)

• Human rights
• Environmental basis

Correlation Coefficients

IQ Correlation in Twins

For siblings raised together:

• Closer the genetic relation, the higher the IQ correlation

For identical twins raised apart:

• IQ correlation higher than fraternal twins raised together

Genetic component in IQ

The Environmental Influence

Non-related children raised in the same home

• No genetic similarity
• Some degree of environmental similarity

Young children

• Average correlation coefficient of +0.30

Older children

• By age 18, -0.03
• Even genetically related children show reduced correlation coefficients as children get older
  • Greater genetic relationship --> less decline

Conclusions:

• High parental influence on IQ when children young

IQ and Race

Genes or environment?

French study

• Lower class children adopted into middle/upper class homes
• Adopted children had IQ of 109
  • 14 points higher than non-adopted lower class children
  • No different than children born to middle/upper class homes

American study

• Black children adopted into white middle/upper class homes
• Adopted children showed significantly higher IQ than non-adopted blacks
  • No different from white children from middle/upper class homes

Conclusion:

• "Racial" differences in IQ due to environmental differences 

Schizophrenia

Affects both sexes equally

1% of the population worldwide

• Constant across cultures
• Another 2-3% have schizotypal personality disorder

Diagnosis

• Psychotic phase
  • Bizarre delusions
  • Prominent hallucinations (usually auditory)
  • Disordered thoughts and incoherence
• Residual phase
  • Eccentric behaviour
  • Socially isolated
  • Poverty of speech
  • Poor attention span

Genes and Schizophrenia

Franz Kallmann (1938)

• 1% rate worldwide
• 15% rate in certain families

Twin studies

• Monozygotic twins
  • Essentially identical genotype
• Fraternal twins
  • Share half their genotype
• If strictly genetic:
  • Monozygotic twins should have same tendency to develop schizophrenia
  • Concordance

Monozygotic twins

• Concordance of 30-50%

Fraternal twins and non-twin siblings

• Concordance of 15%

General population

• Concordance of 1%

Conclusions:

• High genetic component
• Not strictly genetic

Environment and Schizophrenia

Could high monozygotic twin concordance be due to:

• Psychological trauma of having a twin with schizophrenia?
• Higher rates of perinatal trauma?

More adoptee studies

• Compare:
  • Schizophrenia in adopted children of schizophrenic biological parents
  • Adopted children of normal parents
• Schizophrenia higher among children whose biological parents had schizophrenia

Conclusion:

• Child rearing plays minor role in development oF schizophrenia

Schizophrenia is not a single gene disorder

Schizophrenia is a polygenetic effect

• Genes and environment interact
• Chromosome 6

Pre-natal flu

• May contribute to some cases of late onset schizophrenia 

Chapter 3 in Capsule

Nature and Nurture

DNA, Chromosomes, Genes, Proteins

Genotype, Phenotype, Dominant, Recessive

Genetic diversity

Mendelian genetics, Punnett squares

Single gene disorders

Chromosome disorders

Polygenetic effects on behaviour

Heritability

Intelligence and IQ

Schizophrenia

Thoughts for the Bus Ride Home

Why are adoption studies so important in psychology?

What does a correlation coefficient tell you?

Luke Skywalker is a powerful Jedi Knight. He is strong in the ways of the Force. Yoda and Obi wan said the Force was strong in Luke's family. Hence, we assume there is a genetic component to being able to use the Force. Let us assume that the Force gene is recessive (otherwise the galaxy would be full of lightsabre swinging Jedi Knights). If Luke's father (the infamous Darth Vader) had been homozygous recessive, and his mother had been heterozygous recessive, what percentage chance was there that Luke would be homozygous recessive for the Force gene? How about for his twin sister, Princess Leia?