1. Myers PSYCHOLOGY Seventh Edition in Modules
Genetic Influences on Behavior
James A. McCubbin, Ph.D.
Clemson University
Worth Publishers
Nature and nurture is one of the most debated issues in psychology.It looks at the effect that our genetics (nature) and our environment (nurture) has on us. A whole field of study, behaviour genetics, focuses on this issue.
Nature consists of the genes that are passed along to you by your parents the moment you were conceived. Nurture is everything that has nothing to do with genes. It includes being exposed to drugs while still in the womb, consuming healthy food and clean water, breathing second hand smoke, making life choices, deciding where to live, and identifying with a particular ethnic or religious group.
In the module you will also learn about genetics, how traits are passed from one generation to another, the similarities that exist between twins, the influences the environment has on us and finally what role culture has on who we are.

2. Genes: Our Biological Blueprint
Chromosomes
threadlike structures made of DNA that contain the genes
DNA (deoxyribonucleic acid)
complex molecule containing the genetic information that makes up the chromosomes
has two strands-forming a “double helix”--held together by bonds between pairs of nucleotides
You have your own unique genetic code. It is found in every cell nucleus. It is made up of 46 chromosomes – 23 that you got from your mother and 23 that you got from your father. These chromosomes are made of molecules called DNA. It is in this DNA that our genes are stored.

3. Genes: Our Biological Blueprint
biochemical units of heredity that make up the chromosomes
a segment of DNA capable of synthesizing a protein
Genome
the complete instructions for making an organism
consisting of all the genetic material in its chromosomes
You have about 30 million genes. Surprisingly 99.9% of everyone’s genes are identical. This is why there is similarity in appearance and behaviour of people around the world. Our genes are responsible for predisposing, or influencing, our appearance and behavior not determining it. Predispositions are passed on from one generation to another through the DNA to future generations. Being predisposed does not necessarily mean that you are going to get it. It means that you have the possibility of developing it. Whether or not the possibility becomes reality depends on your environment.
For example, you may be predisposed to sunburn easily. Whether or not you burn will depend on your exposure to the sun’s rays. You may be predisposed to bipolar disorder. This means that you have the possibility of developing the disorder as a result of environmental factors.

4. Genes: Their Location and Composition
Nucleus
Chromosome
Gene
Cell
DNA

5. Evolutionary Psychology
Natural Selection
the principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations
Mutation
a random error in gene replication that leads to a change in the sequence of nucleotides
the source of all genetic diversity
Nature and Similarity
We are all very similar. Evolutionary psychologists believe that some of our shared similarities come from genes that have changed to help our ancestors face and conquer problems. People who carried these genes would be more likely to stay in the gene pool to pass the genes on to the next generation. The concept of natural selection says that the traits that we inherit, those that contribute to survival, are most likely to be passed on to future generations. We all have a bit of our previous generations in us.

6. Evolutionary Psychology
the study of the evolution of behavior and the mind, using the principles of natural selection
Gender
in psychology, the characteristics, whether biologically or socially influenced, by which people define male and female

7. Behavior Genetics Behavior Genetics Environment
study of the relative power and limits of genetic and environmental influences on behavior
Environment
every nongenetic influence, from prenatal nutrition to the people and things around us

8. Behavior Genetics Identical Twins Fraternal Twins
Same
sex only
Same or
opposite sex
Identical Twins
develop from a single fertilized egg that splits in two, creating two genetically identical organisms
Fraternal Twins
develop from separate eggs
genetically no closer than brothers and sisters, but they share the fetal environment
Nature and Individual Differences
Our genetic similarity is amazing but so are our differences. Behaviour geneticists study differences in humans by looking at twins and people who were adopted.
Twin Studies
Nature has given us human lab participants – twins.
Identical twins are genetically the same because they came from the same fertilized egg.
Fraternal twins develop from two different fertilized eggs and aren’t any more alike than any two other siblings.

9. Behavior Genetics Temperament Heritability
a person’s characteristic emotional reactivity and intensity
Heritability
the proportion of variation among individuals that we can attribute to genes
may vary, depending on the range of populations and environments studied
Researchers study the heritability of traits. Heritability looks at the differences in our traits or characteristics that are passed on in our genes. A behaviour geneticist might set up a study of identical and fraternal twins to study heritability. They would:
Collect and compare data from identical twins raised in the same home.
Collect and compare data from fraternal twins raised in the same home.
Compare the similarities of the identical twins with the similarities of the fraternal twins.
Research has found that there is a genetic influence on personality traits. This means that identical twins are far more similar in personality than fraternal twins.
Research has also shown that environment plays a key role as well. Studies on twins that were separated at birth and raised apart from each other, have demonstrated that no trait is completely inherited. The behaviours of identical twins are not identical.
Adoption Studies
Another way to look at the nature-nurture issue is to look at adoption studies. Studies have shown that adopted children share more personality trait similarities with their biological parents than with their adoptive parents.
Adoptive parents play a major role in the development of belief systems and in the development of behaviours that are important in being a good citizen.
Both twin and adoption studies have shown that both nature and nurture are important in determining who we are.

10. Behavior Genetics Interaction Molecular Genetics
the dependence of the effect of one factor (such as environment) on another factor (such as heredity)
Molecular Genetics
the subfield of biology that studies the molecular structure and function of genes