Psych lecture October 10 , 2013
• Genetic base of intelligence
• Genetic disorders
• How do I estimate heritability?
• Is intelligence heritable?
• What is the cause of genetic disorders?
Next Time: Evolution & Behavior. Scan and finish chapter 4
Reviewed the difference between genotype and phenotype, dominant and recessive
Polygenetic effects – traits related to action of more than 1 gene or chromosome.
H = variance due to genes/total variance
Estimate of how much observed variability due to genetic factors alone.
H = 0 (due to environment)
H = 1 (due to Genes)
• Does NOT indicated extent to which genes are responsible for expression of trait
• Taps relative contribution of genes to overall variation in population
• All h is telling you is how much is due to environment vs. genes not phenotypic or
• Applies to groups not individuals
Example: the black hair colour of Inuit’s:
If everybod2 has the same trait and nothing changes, there is no heritability so the answer
would be h =0
• H increases as genetic diversity increases
• H decreases as environmental diversity increases
Differences within groups is due to genetics
Differences between groups is due to the environment
Heritability of Intelligence – family relationship study
• Identical twins are 100% related
• Fraternal twins are 50% related
• Parents are siblings are 50% related
• Grandparents, uncle, aunt are 25% related
• 1 cousin are 12.5% related
Bouchard –twins that were separated at birth and then met each other years down the road:
• Bouchard claims that they still have remarkable similarities even though they’ve never
• Twins had similar medical history, both had dogs named toy, both chewed finger nails,
both married a woman named Linda, both had son named Allen, both divorced and
remarried a woman with the same name.
Galton wrote a book called Hereditary Genius in 1869
• Looked if sons of intelligent people we’re intelligent and successful; and they were
• Adopted sons of intelligent men were not
• Measured simple motor and sensory abilities (reaction times) faster you react: higher the
• Believes that i