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Chapter 3

45Ch.3BiologicalFoundations.docx.pdf


Department
Psychology
Course Code
PSY100H1
Professor
Dan Dolderman
Chapter
3

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What Is the Genetic Basis of Psychology?
Genetics (in Psychology): The processes involved in turning
genes “on” and “off”.
Environment affects our genes; how they are expressed and
therefore how they influence our thoughts, feelings, and behaviour,
but genetic tendency often determine the environment we select
for ourselves so biology and environment mutually influence each
other. (Details in notes below.)
Within every cell in the body is the genome, genetic makeup, for making the
entire organism.
Each cell has a certain option (what they do) but this depends
on the environment because the environment determines which
options are taken (what genes are turned on and off in a cell).
Within each cell are chromosomes, structures made of genes.
Typical human has 23 pairs of chromosomes, half of each pair
coming from each parent.
Genes are components of DNA, and the sequence of the genes
produces a certain protein which carries out a specific task.
The environment determines what protein is produced and
when.
As mentioned above, although each cell in the body contains the
same DNA, cells become specialized depending on which genes are
expressed.
Gene expression determines body’s basic physical makeup
and also specific developments throughout life and is involved
in all psychological activity, ex. Learn, fall in love etc.
The Human Genome Project: Map out entire structure of DNA / To identify
the precise order of molecules that make up each of the thousands of genes
on each of the 23 chromosomes. Humans have just over 20,000 genes.
Humans complexity is not due to the number of genes but rather to
how these genes are expressed and regulated.
With the Human Genome Project, researchers are now
comparing different individual’s genomes to how they vary,
specifically how variations in individuals genes determine
whether someone is likely to develop specific disease or have
some special ability.
Heredity Involves Passing Along Genes through Reproduction
Gregor Mendel was the first to discover clues to the mechanisms
responsible for heredity (transmission of characteristics from parents to
offspring by means of genes.)

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He developed selective breeding, that controlled which plants
bred with which other plants. He cross pollinated two different
colored flowers (purple and white) to see what colour flower
would be produced. First generation either completely white or
completely purple. Second generation plants were purple flowers
were produced 75% of the time because plants contained separate
units (genes) existing in different variations (colours). Purple was
dominant, gene expressed in offspring whenever present, and white
was recessive, only expressed when matched with a similar gene
from the other parent.
Genotype: Organism’s genetic makeup determined at the moment of
conception.
Phenotype: Observable physical characteristics resulting from both
genetic and environmental influences (ex. Skin colour may vary due to the
sun, environmental influence).
Polygenic Effects: When a population displays a range of variability for
a certain characteristics. Ex. Height or intelligence.
This variety, of for example skin colour (phenotype), is not the end
product of a single dominant/recessive gene pairing (genotype) but
rather shows the effects of multiple genes.
Genotypic Variation is Created by Sexual Reproduction
Siblings are different from each other (hair colour, eye colour, height,
personality etc.) due to the specific combination of genes, determined by
random cell division before reproduction.
In each parents, reproductive cells divide to produce gametes,
the egg and sperm cells, each of which contains half of every
chromosome pair. After one of each cell combines a zygote
is formed. There are about 8 million combinations of the 23
chromosomes are possible.
The zygote grows through cell division, which is the basis of life.
Errors can occur which lead to mutations. Most have little to no
influence, but some mutations can be adaptive (mutations that help
survival so will be passed onto future generations) or maladaptive
(ones that can lead to disease and possibly death).
Recessive maladaptive genes do not interfere with most
people’s health, only when they are dominant do they affect
people.
Genes Affect Behaviour
Behavioural Genetics: Study of how genes and environment interact to

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influence psychological activity.
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