Genes, Evolution and Behaviour
- Our physical development is in part directed by a genetic blueprint passed down to us
by our parents which set limits on our behavioural capabilities.
- Our genetics combine with environmental factors to determine our behaviour.
- Nature and nurture both play roles, but to what extent is the question.
- Psychologists working in the field of behaviour genetics study the ways in which
favourable and unfavourable environmental conditions can affect the genetically
inherited potential of an organism.
Chromosomes and Genes
- Hippocrates was the first one to suggest that semen contains ‘some sort of design for
the formation of the offspring’ which would be proved 22 centuries later by Gregor
Mendel. Mendel proved that heredity involves passing on of specific organic factors, not
a simple blending of the parents’ characteristics. These characteristics might be visible
in the child, or they might just be there for passing on to later generations.
- Offspring of one set of parents don’t inherit all the same traits, as is shown in the
differences between siblings.
- Genotype: The specific genetic makeup of the individual
- Phenotype: observable characteristics produced by the genetic endowment.
- In a genotype, some of the characteristics or used on only one occasion, some on
another; some are not used at all, because maybe the environment never calls them
- Genotypes are present from birth and never change.
- Phenotypes can be affected by other genes and by the environment.
- Chromosome: Tightly coiled molecule of deoxyribonucleic acid (DNA) that is partly
covered by protein. The DNA part of the chromosome carries the genes, which carry
info about your characteristics, potentials and limitations.
- Every cell in the human body has 46 chromosomes, except for the sex cell which has
23 chromosomes. When the two come together they form a new chromosome of 46 (so
half of your genes come from your dad, the other half from your mom.
- Union of sperm and egg can result in 70 trillion potential genotypes, accounting for the
great diversity in characteristics even in siblings.
- Gene’s affect our body’s development/functioning by coding for the production of
- Proteins control the structure of cells and the chemical reactions that happen in
these cells. Each gene carries the code for a specific protein type (when the
gene is activated, the protein is produced).
- Due to metabolic or environmental factors, proteins are turned on or off. When
turned on, the proteins are produced, and when turned off, the levels of the
protein will decrease. - As protein levels within a neuron change, there is a corresponding change in
the function of that neuron and of the neural circuits it participates in.
Dominant, Recessive and Polygenic Effects
- Genotype and Phenotype aren’t identical because some genes are dominant and
some are recessive.
- If a gene received from the mother/father is dominant, the characteristic that it controls
will be displayed.
- If the gene is recessive, the characteristic won’t show up unless the partner gene from
the other parent is also recessive.
- Brown eyes and dark hair are dominant over blue eyes and fair hair, so the only
possible way for someone to have blue eyes is if the parents both have genes for blue
eyes that were passed down to you.
- Recessive genes can still be passed down to offspring even if they don’t show up.
- Polygenic Transmission complicates the straightforward picture that would occur if
all characteristics were determined by one pair of genes. A number of gene pairs
combine their influences to create a single phenotypic trait.
Mapping the Genetic Code
- The genetic structure in every one of the 23 pairs of chromosomes has been mapped
using methods that allowed the researchers to literally disassemble the genes and study
the specific sequence of substances that occur in each gene.
- The found that humans have less genes than expected: the same amount as a fruit fly.
- About 200 genes may have arisen from genes that bacteria inserted into our early
Genetic Engineering: The Edge of Creation
- Recombinant DNA Procedures: Genetic DNA is cut into pieces by enzymes,
combined with DNA from another organism, and inserted into a host organism, such as
bacterium. Now inside the host, this new DNA combination divides and produces copies
- This procedure has been used to produce human growth hormone, which is
hard to naturally produce and collect in great quantities. By producing it through
recombinant DNA procedures, 121 children were able to be treated who were
deficient in this hormone.
- We can now insert new genetic material into viruses that can infiltrate neurons and
modify their genetic structure.
- Recent gene modification research has focused on processes like learning, memory,
emotion and motivation.
- Gene Knockout Procedure: Altering a gene that prevents it from carrying out its
normal function. The function of the gene is eliminated. So genetic material can be
inserted to prevent neurons from responding to a neurotransmitter, then measure to see if the animal’s learning or memory is affected by it. This can help determine the
importance of specific neurotransmitters substances in relation to behaviours of interest.
- Great care needs to be taken when interpreting the outcome of Gene Knockout
studies because it’s rare that a behaviour is controlled by a single gene. So the
disruption of behaviour after a gene knockout may help to identify one of the
genes involved in the behaviour, but this doesn’t mean that the gene is wholly
responsible for the behaviour.
- Also sometimes knocking out a single gene can result in disruption of a wide
range of functions.
- Gene modification techniques may one day enable us to alter genes that
contribute to psychological disorders like schizophrenia.
- Genetic engineering gives humans potential control over the processes of heredity and
evolution which give birth to a whole bunch of moral and ethical issues. Should we use
these techniques to clone people? Extend lifespan?
- Heredity potential is carried within the DNA portion of the 23 pairs of chromosomes in
units called genes. GEnotype and phenotype are not identical because some genes are
dominant while others are recessive. Many characteristics are polygenetic in origin, i.e.
influenced by interactions of multiple genes.
- Genes influence the development, structure, and function of our body, including our
brain, by controlling the production of proteins.
- Genetic engineering allows scientists to duplicate and alter genetic material or,
potentially, to repair dysfunctional genes
Behaviour Genetics Techniques
- Knowledge of the principles of genetic transmission tells us how genetically similar
people are, depending on their degree of relatedness to each other.
- Since children get half of their genetic material from each parent, the chance of
sharing a gene with one of your parents is 50%, or .50. Siblings also have a 50%
chance of sharing a gene with you.
- Behaviour geneticists are interested in studying how hereditary and environmental
factors combine to influence psychological characteristics.
- Heredity: the passage of characteristics from parents to offspring by way of genes.
- Heritability: how much of the variation in a characteristic within a population can be
attributed to genetic differences. Refers to differences, or variance, in the trait across
individuals, not the trait itself.
- If weight has a heritability coefficient of .60, that doesn’t mean that 60% of my
body weight is due to genes and 40% is due to environment. The heritability
coefficient is a way of predicting how much variation is attributable to genetic
- Heritability applies only to differences within a group, not to differences between
groups. - It’s important to recognize the group of people that was studied because if you
wanted to obtain a heritability coefficient for intelligence from a group of highly
advantaged children (plentiful resources, education support) the coefficient
would be very high, but if you studied a group of children from diverse
backgrounds (poor to rich) the coefficient would be lower.
- Heritability Coefficient is a sta