Transcript The Genetic of Behavior

Chapter 1
The Major Issues
The Mind-Brain Relationship
• Biological Psychology is the study of the
physiological and genetic basis of behavior.
• Emphasis is placed upon physiological,
evolutionary and developmental mechanisms
of behavior.
• A strong emphasis is placed upon brain
functioning.
Fig. 1-1, p. 2
The Mind-Brain Relationship
• Brain functioning can be explained at a more
microscopic level in terms of neuron and glia
activity.
Fig. 1-2, p. 3
The Mind-Brain Relationship
• Biological explanations of behavior fall into
four categories:
– Physiological- emphasis on brain and other
vital organs.
– Ontogenetic- describes the development of
a structure or behavior.
– Evolutionary- focuses upon the
evolutionary history of a behavior.
– Functional- describes why a structure or
behavior evolved as it did.
The Mind-Brain Relationship
• Deep understanding of a particular behavior
is tied to being able to explain the behavior
from each of these perspectives.
The Genetics of Behavior
• Both genes and environment interact to
shape human behavior.
• The fundamental issue is how much a role
genetics do play in shaping human behaviors.
– Examples: psychological disorders, weight
gain, personality, sexual orientation?
The Genetics of Behavior
• Genes are basic units of heredity that
maintain their structural identity from one
generation to another.
• Genes are aligned along chromosomes
(strands of genes) and come in pairs.
The Genetics of Behavior
• A gene is a portion of a chromosome and is
composed of deoxyribonucleic acid (DNA).
• DNA serves as a model for the synthesis of
ribonucleic acid (RNA).
Fig. 1-7, p. 12
The Genetics of Behavior
• RNA is a single strand chemical that can
serve as a model for the synthesis of
proteins.
• Proteins determine the development of the
body by:
• forming part of the structure of the body.
• serving as enzymes that serve as
biological catalysts and regulate chemical
reaction in the body.
The Genetics of Behavior
• Homozygous for a gene means that a person
has an identical pair of genes on the two
chromosomes.
• Heterozygous for a gene means that a
person has an unmatched pair of genes on
the two chromosomes.
The Genetics of Behavior
•
Some genes can be either dominant or
recessive.
– Examples: eye color, breast cancer
genes, ability to taste PTC, curly hair
• A dominant gene shows a strong effect in
either the homozygous or heterozygous
condition (DD, Dd, or dD).
• A recessive gene shows its effect only in the
homozygous condition (dd).
Fig. 1-8, p. 13
The Genetics of Behavior
• Each chromosome participates in
reproduction independently of the others.
• Each species has a certain number of
chromosomes.
• Crossing over occurs when a pair of
chromosomes break apart during
reproduction and reconnects and attaches to
the second chromosome.
– BC & bc  Bc & bC
The Genetics of Behavior
• Types of genes include:
– Autosomal genes - all genes except for
sex- linked genes.
– Sex-linked genes - genes located on the
sex chromosomes.
• In mammals, the sex chromosomes are
designated X & Y.
– Females have two X chromosomes (XX).
– Males have an X and a Y chromosome
(XY).
The Genetics of Behavior
• During reproduction:
– Females contribute an X chromosome.
– Males contribute either an X or a Y
chromosome that determines the sex of
the child.
• If an X chromosome is contributed by the
male, the off-spring is female.
• If a Y chromosome is contributed by the male,
the off-spring will be male.
The Genetics of Behavior
• The human Y chromosome has genes for 27
proteins
• The human X chromosome has genes for
approximately 1500 proteins.
• Thus, sex-linked genes usually refer to Xlinked genes. (Example: Red-green color
deficiency, Hemophilia)
• Sex-limited genes are genes that are present
in both sexes but mainly have an effect on
one sex (Chest hair, breast size, etc.)
The Genetics of Behavior
• Sources of variation in a species that allows
for evolution to occur include:
• Recombination refers to a new combination
of genes in the off-spring that yield
characteristics not found in either parent.
• Mutation refers to a change in a single gene
that is rare, random and often independent of
the needs of the organism.
The Genetics of Behavior
• Almost all behaviors have both a genetic
component and an environmental
component.
• Researchers study monozygotic and fraternal
twins to infer how much of a genetic
component exists for a particular behavior.
• Researchers also study adopted children and
their resemblance to their biological parents
to infer the influence of heredity.
The Genetics of Behavior
• Heritability
• Estimates of hereditary influences are often
difficult to infer and are prone to error.
• Sources of error include the following:
– The inability to distinguish between the
effects of genes and prenatal influences.
– Environmental factors can inactivate
genes.
The Genetics of Behavior
• Sources of error (con’t)
– Multiplier effect – genetic tendencies that
guide behavior will result in a change in the
environment that magnifies the original
tendency.
– Traits with a strong hereditary influence
can by modified by environmental
intervention.
• e.g. PKU---phenylketonuria
The Genetics of Behavior
• Genes do not directly produce behaviors.
• Genes produce proteins that increase the
probability that a behavior will develop under
certain circumstances.
• Genes can also have an indirect affect.
– Genes can alter your environment by
producing behaviors or traits that alter how
people in your environment react to you.
The Genetics of Behavior
•
Evolution refers to a change in the
frequency of various genes in a population
over generations
• Evolution attempts to answer two questions:
1. How did some species evolve?
2. How do species evolve?
The Genetics of Behavior
•
How species did evolve involves the
tentative construction of “evolutionary trees”.
• How species do evolve rests upon two
assumptions:
1. Offspring generally resemble their
parents for genetic reasons.
2. Mutations and recombination of genes
introduce new heritable variations that
help or harm the chance of survival and
reproduction.
The Genetic of Behavior
• Common misconceptions about evolution
include the following:
– Lamarckian evolution - “The use or disuse
of some structure or behavior causes an
increase or decrease in that behavior.”
– “Humans have stopped evolving.”
– “Evolution means improvement.”
– “Evolution acts to benefit the individual or
the species.”
The Genetics of Behavior
• Evolutionary psychology (sociobiology)
focuses upon functional explanations of how
behaviors evolved.
• Assumes that behaviors characteristic of a
species have arisen through natural selection
and provide a survival advantage.
– Examples: differences in peripheral/color
vision, sleep mechanisms in the brain,
eating habits, temperature regulation.
The Genetics of Behavior
• Some behaviors are more debatable
regarding the influence of natural selection.
• Examples include:
– Life span length
– Gender differences in sexual promiscuity
– Altruistic behavior
The Use of Animals in Research
• Animal research is an important source of
information for biological psychology but
remains a highly controversial topic.
• Animal research varies on the amount of
stress and/ or pain that is caused to the
animal itself.
The Use of Animals in Research
•
Reasons for studying animals include:
1. The underlying mechanisms of behavior
are similar across species and often
easier to study in nonhuman species.
2. We are interested in animals for their own
sake.
3. What we learn about animals sheds light
on human evolution.
4. Some experiments cannot use humans
because of legal or ethical reasons.
Fig. 1-12, p. 23
The Use of Animals in Research
• Justification for research considers the
amount of benefit gained compared to the
amount of distress caused to the animal.
– No clear dividing line exists.
• Colleges and research institutions in the
United States are required to have an
Institutional Animal Care and Use Committee.
– Oversees and determine acceptable
procedures.