PSYC 100 Study Guide - Epigenetics, Lewis Terman, Meiosis

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Published on 10 Apr 2013
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Week Two: Genetics and Intelligence
How is the heritability of intelligence connected with the heritability of other
behavioural and human factors we have studied so far?
Genetics and Environment
How are behaviours and other traits inherited?
Behaviour Genetics study of genetic influences on behaviour (e.g. someone with alcoholic parents will
be more sensitive to alcohol, but must still make the decision to drink)
Our genetic material, or DNA, is organized into structures called chromosomes that are in the nucleus of
every cell, and is a combination of genetic material from the two parents
A human has 23 pairs of chromosomes (22 autosomes, 1 pair made up of the X and Y sex
chromosomes males have an XY pair, females have XX)
Sperm and egg cells only have half of each pair of chromosomes (through a process called
meiosis), so when they combine there is a cell with a complete set of chromosomes.
The egg can have only an X chromatid, therefore the sperm’s X or Y determines the sex
Genes can be defined as regions of chromosomes that encode (transfer genetic information
from DNA) particular proteins
The point where a particular gene is located on the chromosome is called the locus the gene
on one chromosome of a pair may or may not be exactly the same as the gene on the other
chromosome at the same locus
o Allele: the pair of genes at a given locus alternative forms of the same gene
o Homozygous: each parent contributes the same allele for a particular gene
o Heterozygous: each parent contributes different alleles for a particular gene
If the alleles are different, one often has a dominant effect over the other
o Dominant: trait exhibited when individual possesses heterozygous alleles at that locus
o Recessive: trait occurs only when it is expressed by homozygous alleles
Genes can influence behaviour, but don’t do so directly genes guide cells to generate proteins that
cause our cells to form chemicals in the body that are related to behaviour, such as neurotransmitters
Any genetic contribution to a trait (structural or behavioural) is the result of certain types of
proteins being manufactured by a given cell
The type of protein that is made depends not only on the structure of a gene but also the
environment (e.g. identical twins grow up differently due to diet, etc.)
Heritability: amount of variability in a given trait in a given population in a given time due to
genetic factors; heritable traits are passed on to subsequent generations by the passage of
genes through sexual reproduction
The Genotype is the genetic makeup of a trait, while the Phenotype is how the trait is expressed
Because the allele for brown eyes is dominant, a person with one allele for brown eyes and one
for blue eyes (Bb) will have the same eye colour as someone with two brown alleles (BB) these
two individuals have the same phenotype but different genotype single-gene effect
Recessive traits show up phenotypically when two recessive traits breed: two brown eyed
parents with genotype Bb can produce blue-eyed (bb) or brown-eyed (Bb or BB) offspring
Most behaviours are caused by the interaction of multiple genes with the environment however,
there are some examples of single-gene mechanisms such as ‘fearfulness’ in dogs, and FOXP2, a gene in
chromosome 7 that is related to speech articulation.
Since most disorders and genetic traits are polygenic instead, Behaviour Geneticists use studies
examining the relationship between genetic similarity and similarity in some trait to gain evidence for
the effects of genes on behaviour.
They use Family Studies, Adoption Studies, and Twin Studies, in which identical (monozygotic) twins,
who have nearly identical genotypes, and fraternal (dizygotic) twins, who are no more genetically similar
than any two siblings, are compared.
If the rate of concordance (matching phenotypes between twins) for a trait is higher for identical
twins than for fraternal twins, then that trait has a genetic component (e.g. intelligence, schizophrenia).
Epigenetics: the study of heritable changes that occur
without a change in the DNA sequence (mutation)
how environment (toxins, stress, diet, etc.) can
influence gene expression and behaviour
Exposure to an external factor may cause a
change in a group of cells or their blueprint…
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)
To summarize / keep in mind
Correlation (most common method of research) shows that two factors are linked, not
necessarily that one cause the other
These studies tell us about population effects, not individual effects (generalized)
Polygenic traits (e.g. height, intelligence) are on a continuum inheritance is not all or nothing
It is not easy to separate nature (genetics) and nurture (environment) since genes can be
changed by the environment
Describes the proportion of the observed variance in a behaviour that can be attributed to
genetic differences among individuals
h2: the statistic used to measure heritability the amount of variability in a given trait in a given
population at a given time due to genetic factors
Iceland will produce higher heritability estimates than Toronto heritability estimates for a
given population or group may not generalize to other populations or groups
Defining Intelligence
Is intelligence best understood as a single trait or as a clus ter of related traits?
Operational definition of intelligence…
Textbook “…a person’s ability to learn and remember information, to recognize concepts and
their relations, and to apply the information to their own behaviour in an adaptive way”
Debates remain around definition and measurement different investigators have different
ideas and different cultures place values on different abilities
To operationally define intelligence you an use a theory to define a measurement scale, then
use scores on that scale as your operational definition…
Differential Approach (Sir Francis Galton)
Devoted to tests and measures of individual differences in various psychological properties,
including problem-solving ability
Galton determined the relationship between intelligence and other biologically based attributes
such as head size, sensory discrimination ability, and “neural quickness” (speed person
processes information) never found any strong relationships
Factor Analysis (Charles Spearman)
A way to determine correlations between individual items on a test if a group of test items
correlate highly with each other, provides evidence they are measuring the same thing
“The indifference of the indicator” content of the test items and the nature of the task used to
test general intelligence doesn’t matter in terms of test scores
Since all measures correlated positively, they must all reflect a common factor of intelligence,
called “g” for general intelligence
Binet-Simon Scale (Alfred Binet and Theodore Simon)
Intelligence as a collection of higher-order mental abilities; interaction with environment is very
important (more than genetics alone)
Developed the test to identify mentally challenged children by assessing scholastic skills
Later introduced the concept of mental age’ into test outcomes was very popular because it
allowed one to easily rank and compare children
Stanford-Binet (revised by Lewis Terman)
Revised the concept of mental age and introduced measure of the Intelligence Quotient (IQ)
mental age divided by chronological age
Ratio IQ is flawed in adults however since mental age eventually stops but chronological doesn’t
Deviation IQ (David Wechsler)
To overcome the problem with Ratio IQ, Deviation IQ compares an individual’s score with those
received by other individuals of the same chronological age
100 is the average score of a given age group, and scores are distributed on a normal curve
around this average point; 15 equals one standard deviation
Wechsler Scales (WAIS and WISC) (David Wechsler)
Believed intelligence is made up of multiple abilities that couldn’t be represented by one score
Divided tasks into Verbal and Performance (nonverbal) with further subscales (e.g. vocabulary)