Week 14: Genetics and Intelligence
Nature Vs. Nurture: Psychologists are now in agreement that all behaviour results from both nature and
Nativism: The philosophical view that we are born with knowledge already present (nature)
Empiricism: The philosophical view that we obtain all knowledge through our senses (nurture)
Behavioural Genetics: The study of genetic influences on behaviour.
• If an individual is born to parents who have alcohol problems, that person could inherit the genes that
create a sensitivity for alcohol, but he or she must decide to go drink.
• Involves the combining of genetic material from a male and a female through the union of a sperm and
an egg (made haploid by mitosis)
• Since the egg only contains XX and the sperm contains XY, the sex is determined by the father
• Even though half your genes come from your mother and half from your father, the way the genes
combine and are expressed is much more complex than attributing half your traits to one parent and
half your traits to the other
Genes and Alleles:
• Genes encode proteins that carry out bodily functions
• The point on a chromosome where a particular gene is located is called a locus (pleural loci)
• When genes at the same locus on 2 chromosomes are the same, they are homozygous at that locus. If
not, they are heterozygous
• The pairs of genes at a locus are called alleles (p. 66) one from the mother and one from the father.
One gene may be dominant over the other.
• The amount of variability in a given trait in a given population at a given time due to genetic factors;
measured as h and sometimes referred to by this measure instead of the word.
Polygenic: A trait that is influenced by more than one pair of genes.
• Ex. Labrador retrievers: the `B` controls fur colour, while the ‘E’ controls the expression of B. The
dominant “B” allele produces black fur, the recessive b allele produces brown fur.
• Will an E (dominant) allele, the fur will remain the colour that the b or B coded for, but if a dog has 2 e
(recessive) alleles, it will be golden regardless of the B or b allele
Single Gene Traits:
• Most behaviours are caused by the interaction of multiple genes with the environment. However there
are some examples of single-gene mechanisms such as the fear gene observed in dogs.
• An example in humans, is the FOXP2 gene, associated with a severe language disorder (p. 73)
Concordance: The expression of similarity in traits (or absence of traits) by both twins.
• Most disorders and genetic traits are polygenic • If the rate of concordance for a trait is higher for identical twins than for fraternal twins, then that trait
has a genetic component. A number of traits such as intelligence and schizophrenia are more likely to
be concordant for identical twins than for fraternal twins, and thus we conclude they have a genetic
Epigenetics: The study of heritable changes that occur without a change in the DNA sequence.
• Most epigenetic changes affect non-reproductive DNA or cause changes in cells that are passed on as
the cells divide asexually.
• Differentiated cells: Less-specialized cells whose profiles or characteristics have, over time, grown
increasingly different from and more specialized than other cells of the same type (e.g., a single-cell
zygote develops into a multicellular zygote).
• Proteome changes dynamically as a response to environment (protein expression)
Errors in Predicting Inheritance:
• Correlation can only tells us whether or not two factors are linked
• Studies tell us about population effects, not individuals
• Polygenic traits such as height or intelligence lie on a continuum of behaviour (not all or nothing)
• Difficult to separate nature and nurture effects
Operational Definition of Heritability:
• Heritability describes the portion of the observed variance in a behaviour that can be attributed to
genetic differences among individuals. You would need a statistical measure that shows variance in
behaviour that can be attributed to genetic differences in a certain population
Heritability, or H : The statistic use