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Chapter 4

Psychology 1000 Chapter Notes - Chapter 4: Social Darwinism, Neuroticism, Polygynandry

Course Code
PSYCH 1000

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Chapter 4
Genes, Evolution, and Behaviour
Chapter 4:
Genes, Evolution, and Behaviour
Genetic Influences
- Genetic endowment combines with environmental forces to determine our
- Psychologists working in the field of behaviour genetics study which
favourable or unfavourable environmental conditions can affect the
genetically inherited potential of an organism
Chromosomes and Genes
GENOTYPE specific genetic make-up of an individual
PHENOTYPE observable characteristics produced by that genetic
- Genotypes are present from conception and never change
- Phenotypes can be affected by other genes and by the environment
- Union of two cells (egg from the mother and sperm from the father) is the
beginning of a new individual
- The egg and sperm carry within them the material of heredity in the form of
rodlike units called chromosomes
CHROMOSOME tightly coiled molecule of DNA that is partly covered by
- DNA portion of the chromosome carries the hereditary blueprint in units
called genes
- Every cell in the human body except one type (sex cell) has 46 chromosomes
- Sex cell has only 23 chromosomes
o 23 chromosomes from the mother and 23 chromosomes from the
sperm to form a new ell
o The new cell (zygote) will have 46 chromosomes
- Genes within each chromosome also occurs in pairs
o Offspring receives one of each gene pair from each parent
o Every cell nucleus in your body contains the genetic code for your
entire body
- The two copies of each gene, one from your mother and one from your
o Alternative forms of a gene that produce different characteristics
- Genes code for the production of proteins
- Each individual gene carries the code for a specific protein
- When the gene is activated, cell produces specified protein
Dominant, Recessive, and Polygenic Effects
- Some genes are dominant and some are recessive
DOMINANT particular characteristic that it controls will be displayed
RECESSIVE characteristic will not show up unless the partner gene
inherited from the other parent is also recessive

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Chapter 4
Genes, Evolution, and Behaviour
POLYGENIC TRANSMISSION when number of gene pairs combine their
influences to create a single phenotypic trait
o Complicates the straightforward picture
Mapping the Genetic Code
- Human Genome Project
- Genetic structure in every one of the 23 chromosome pairs has been mapped
by using methods
- Allowed researchers literally to disassemble the genes on each chromosome
o Study the specific sequence of substances
- Human Genome Project discovered that humans have 25000 genes
Genetic Engineering: The Edge of Creation
- Recombinant DNA procedures allow researchers use certain enzymes to cut
the long threadlike molecules of genetic DNA into pieces
o Combine them with DNA from another organism and insert them into
a host organism
- New DNA combination continues to divide and produce many copies of itself
- This procedure used to produce the human growth hormone
o Difficult to obtain naturally in large enough quantities to use for
therapeutic purposes
- Gene knockout is a procedure where that particular function of the gene is
o Can help psychologists determine the importance of particular
transmitter substances in relation to the behaviours of interest
- Very few behaviours are controlled by a single gene
- Disruption of a behaviour after a gene knockout may help to identify one of
the genes involved in the behaviour
o This identification does not mean that one gene is wholly responsible
for the behaviour
- Knocking out a single gene may disrupt a wide range of functions
Behaviour Genetic Techniques
- Principles of genetic transmission tells us how genetically similar people are
- Hereditary and environmental factors combine to influence psychological
HEREDITY passage of characteristics from parents to offspring by way of
HERITABILITY much of the variation in a characteristic within a population
can be attributed to genetic differences
- Heritability applies only to differences within a group, not to differences
between groups
- If there is a higher concordance in people who are more highly related to one
o Then this points to a possible genetic contribution
o Especially if the people have lived in different environments

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Chapter 4
Genes, Evolution, and Behaviour
- Adoption Study
o A person who was adopted early in life is compared on some
characteristic both with:
The biological parents who the person shares genetic
The adoptive parents whom no genes are shared
o If the adopted person is more similar to the biological parents then
genetic influence is suggested
o If the adopted person is more similar to the adoptive parents then
environmental influence is suggested
- Twin Study
o Monozygotic (identical) twins develop from the same fertilized egg
Genetically identical
o Dizygotic (fraternal) twins develop from two fertilized eggs
Share 50% of genetic endowment
o Twins are usually raised in the same familial environment
o If the identical twins are far more similar to each other than are the
fraternal twins
Genetic factor is likely to be involved
Possibility that identical twins are more similar because they
look alike and might be treated more alike so share a similar
- Both adoptive and twin studies led behavioural geneticists to conclude that
many psychological characteristics
o Include intelligence, personality traits, certain psychological disorders
o Have notable genetic contribution
- Behaviour genetics studies also have demonstrated that environmental
factors interact with genetic endowment in important ways
Genetic Influences on Behaviour
- Unique characteristics as individuals arise from combination of our learning
- Environment in which we behave acting on a substrate provided by our
genetic makeup
Heredity, Environment, and Intelligence
- Genetic argument:
o Intelligence is totally determined by genes
o Two individuals with exactly the same genes would have identical test
o Non-identical brothers and sisters share only half their genes
o Correlation between the test scores of fraternal and other siblings
should be lower
o Data:
Correlations between the test scores of identical twins are
substantially higher than any other correlations
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