LAW 122 Chapter Notes - Chapter 4: Seymour S. Kety, Phenotypic Trait, Nucleic Acid Structure
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Psychology Chapter 4 Notes
Our genetic endowment combines with environmental forces to determine our behavior
Chromosomes And Genes
Hippocrates suggested that semen contains not body parts, but rather some sort of design for the formation of offspring
Gregor Mendal, a monk whose research with garden peas in the 1860’s marked the beginning of modern genetic theory
Mendal showed that heredity involves the passing on of specific organic factors, not a simple blending of the parents’
The offspring of one set of parents do not all inherit the same traits as is evident in the differences we see among brothers
Genotype= the specific genetic makeup of an individual
Phenotype= the observable characteristics produced by that genetic endowment.
Some are used at one occasion; others are never used at all, either because they are contradicted by other genetic directives
or because the environment never calls them forth. Thus genotypes are present from conception and never change, but
phenotype s can be affected by other genes and by the environment.
Chromosome=A tightly coiled molecule of DNA that is partly covered by protein
The DNA portion of the chromosome carries the hereditary blueprint in unites called genes. In humans, every cell has 46
The sex cell which is the only exception has 23
The 23 from the egg combines with the 23 of the sperm creating a zygote
Zygote= contains 46 chromosomes
The genes within each chromosome also occurs in pairs so that the offspring receives one of each gene pair from each
Every cell nucleus in your body contains the genetic code for your entire body. In all these cells (except for egg and
sperm), there are 2 copies of each gene, one from your mother and one from your father. Alternative forms of a gene that
produce different characteristics are called Allels
Genes affect our body’s development and functioning through our general mechanism: genes code for the production of
Approximately 70,000 different types of proteins are found in a human control the structure of individual cells and all the
chemical reactions that go on within those cells, whether they are reaction necessary to sustain the life of the cell, or are
changes induced periodically by experience or maturation. It is estimated that about half of all genes target brain structure
and function. Each individual gene carries the code for a specific protein, and when that gene is activated, the cell produces
the specified protein. At different points in development, in response to different environmental factors a gene may be
activated and a protein produced or an already active gene may be “turned off” and the levels of a specific protein will then
decrease. As the protein levels within a neuron change, there is a corresponding change in the function of that neuron and
the neural circuits in which it participates.
Dominant, Recessive, and Polygenic Effects
If a gene in the pair received from the mother and father is dominant, the particular characteristic that it controls will be
displayed; is the gene is recessive, the characteristic will not show up unless the partner gene inherited from the other
parent is also recessive
In greater many instances, a number of genes pairs combine their influences to create a single phenotypic trait. This action
is also known as polygenic transmission, and it complicates the straightforward picture that would occur if all
characteristics were determined by one pair of genes.
The discovered humans have fewer genes than expected; a human has approximately 25,000 genes and not the 100,000
Genetic Engineering: The Edge Of Creation
To duplicate and modify the structure of genes themselves. In recombinant DNA procedures, researchers use certain
enzymes to cut the long threadlike molecules of genetic DNA into pieces, combine them with DNA from another
organism, and insert them into a host organism, such as a bacterium. Inside the host, the new DNA combination continues
to divide and produce many copies of it self.
Scientists have used this procedure to produce human growth hormones
Molecular biologists have developed methods for inserting new genetic material into viruses that can infiltrate neurons and
modify their genetic structure.
Altering a specific gene in a way that prevents it from carrying out its normal function= Gene Knockout, because that
particular function of the gene is eliminated. The effects on behavior are then observed
Loss of the serotonin reuptake mechanism results in serotonin remaining in the synapse after its release and a consequent
alteration in the activity of serotonin releasing neurons and serotonin receptors.
Very few behaviors are controlled by a single gene
If a behavior does occur, it doesn’t mean that that single gene was responsible.
It may disrupt a wide range of functions
Genetic engineering gives humans potential control over the processes of heredity and evolution
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
polygenic origin that is influenced by interactions of multiple genes.
Genes influence the development, structure and function of our body, including our brain by controlling the production of
Genetic engineering allows scientists to duplicate and alter genetic material or, potentially, to repair dysfunctional genes.
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Behavior Genetics Techniques
Knowledge of the principles of genetics transmission tells us how genetically similar people are depending on their degree
of relatedness to one another
Children get half of their genetic material from each parent.
From grandparents we get a chance of 0.25% to inherit their genes.
Behavior genetics are interested in studying how hereditary and environmental factors combine to influence psychological
The extent to which variation in a particular characteristic within a group can be attribute to genetic factors is estimated
statistically by a heritability coefficient
Heredity= the passage of characteristics from parents to offspring’s by way of genes; heredibility means how much of the
variation in a characteristic within a population can be attributed to genetic differences
It is important to note that heredibility refers to differences or variance, in the trait across individuals and not to the trait
Hereditability applies only to differences within a group not to differences between groups.
Important to know what group was studied
The hereditability coefficient is a statistical estimate of how much of the variability within a group is due to genetic factors.
If the environment does not account for the variation in intelligence within this group, then the difference could be due to
genetic factors and the heredibility coefficient would estimate a high value
If a characteristic has higher concordance, or co-occurrence, in people who are more highly related to one another then
this points to a possible genetic contribution, particularly if the people have lived in different environments.
One research method based on this principle is the adoption study, in which a person who was adopted in early life is
compared to some characteristics both with biological parents with whom the person shares genetic endowment, and with
the adoptive parents, with whom no gene are shared.
Seymour Kety and coworkers (1978) identified formerly adopted children who were diagnosed with the disorder later in
The researchers found that 12% of biological family members also had been diagnosed with schizophrenia, compared with
a concordance rate of only 3% of adoptive family members suggested a hereditary link
Twin Studies= are one of the more powerful techniques used in behavior genetics. Monozygotic (identical twins) develop
from the same fertilized egg, so they are genetically identical.
Dizygote= (fraternal) twins develop from two fertilized eggs so they share 50% of their genetic endowment
Sometimes they are able to find and compare sets of identical and fraternal twins who were separated very early in life, and
raised in different environments
Both adoption and twin studies have led behavioral genetics to conclude that may psychological characteristics, including
intelligence, personality traits and certain psychological disorders have a notable genetic contribution.
Behavior genetics studies have demonstrated that environmental factors interact with genetic endowment in important
The level of criminality was highest of all for those sons whose biological and adoptive fathers both had criminal records,
suggesting a combined impact of genetic environmental factors.
The field of behavior genetics studies contributions of genetic and environmental factors in psychological traits and
behaviors. The major research methods used in attempts to disentangle heredity and environmental factors are adoption and
twin studies. The most useful research strategy in this area is the study of identical and fraternal twins who were separated
in early life and raised in different environments
Behavior genetics techniques allow a hereitability coefficient to be determined for different characteristics. The heredibility
coefficient indicates the extent to which variation in a particular characteristic can be attributed to genetic factors.
Genetic Influences on Behavior
All our behaviors reflect the interaction between genes and the environment
The more genes people have in common the more similar they are in IQ
Biological Reaction Range, The Environment, Personality, and intelligence
The reaction range for a genetically influenced trait is the range of possibilities- the upper and lower limits- that the genetic
code allows, thus, to say that intelligence is genetically influenced does not mean that intelligence is fixed at birth. Instead,
it means that an individual inherits a range for potential intelligence that has upper and lower limits. Environmental effects
will then determine where the person falls within these genetically determined boundaries. Each of us has a range of
intellectual potential that is jointly influenced by 2 factors: our genetic inheritance and the opportunities our environment
provides for acquiring intellectual skills.
Intellectual growth depends not only on genetic endowment and environmental advantages but also on interests motivation
and other personal characteristics that affect how much we apply ourselves or take advantage of our gifts and opportunities
Behavior Genetics And Personality
Hans Eysenck was one of the first modern personality theorists to suggest to biological basis for major personality traits.
Eysenck argued that personality differences could be traced to differences in the brain development or function. The
personality dimension extraversion- introversion
One prominent personality trait theory is called five factor model. 5 factor model such as Robert McCrae and Paul Costa
believe that individual difference in personality can be accounted for by variation along 5 broad personality dimensions or
traits known as the big 5:
o Extraversion- Introversion = sociable, outgoing, adventurous versus, quiet, inhibited, solitary)
o Agreeableness= (cooperative, helpful, good natured versus antagonistic, uncooperative, suspicious)
o Consciousness= (responsible, goal directed, dependable versus undependable careless, irresponsible)
o Neuroticism= (worrying, anxious, emotionally unstable versus well adjusted, secure, calm)
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