ap psych study guides

🤔  Unit 5: Cognitive Psychology

👶  Unit 6: Developmental Psychology

🤪  Unit 7: Motivation, Emotion, & Personality

🛋  Unit 8: Clinical Psychology

2.1 Interaction of Heredity and Environment


⏱️  4 min read

written by

Megan Revello

megan revello

Dalia Savy

dalia savy


  • biological psychology

  • chromosomes

  • genome

  • molecular genetics

  • epigenetics

  • evolutionary psychology

  • behavior genetics

  • DNA

  • identical (monozygotic) twins

  • heritability

  • natural selection

  • environment

  • genes

  • fraternal (dizygotic) twins

  • interaction

  • mutations

Basics of Biology

  • In this key topic, it is important to remember that the environment🌳 is every external influence that exists. The environment often influence religion, politics, and our morals.

  • We all have 46 chromosomes (23 pairs) in each cell. These chromosomes are structures made up of DNA🧬 that contain our genes, which are studied in this chapter.

    • There are both expressed/active genes and inactive genes, which depends on your environment.

  • A genome is all of the genes that make up an organism.

Heredity and the Environment

An essential question that faces psychologists is the nature vs. nurture debate. Are we more influenced by our genes and heredity🧬 or by our experiences🧠?  Biological psychologists in particular are interested in studying the links between our biological (genes, neurons, etc.) processes and psychological processes. 

  • One group of behavioral psychologists, behavior geneticists, are interested in studying the power and limits of genetic and environmental influences on behavior. To do this we may look at mutations, chromosome pairs, DNA, genes, or even the entire human genome to see where minute differences can come into play. 

  • Another important way that psychologists can study the influence of nature vs. nurture is through twin and adoption studies. If we are able to study identical twins that were separated at birth, we can compare and contrast them. We would look for similarities and differences in their abilities, personalities, and traits to get an idea of what was more influential - nature or nurture. We can further make comparisons between fraternal twins and siblings raised in the same family to gain additional insights.  

    • Identical (monozygotic) Twins develop from the same fertilized egg that eventually splits into two. Each twin has the same genes, but not the same number of copies of those genes. This may explain some small differences between the two twins or why one is more at risk for illnesses. Identical twins also share the same prenatal environment (placenta) but one may receive slightly better nourishment and care.

    • Fraternal (dizygotic) Twins develop from different fertilized eggs.

  • We can also use heritability to understand the variations that exist between individuals being studied. Heritability basically tells us how much of the variation that exists between a group of individuals is due to genetics. Heritability is NOT the amount or percent of a given trait that is inherited. It is instead an explanation of the differences that exist between us related to genetic factors.


Image Courtesy of Study

  • There are also molecular geneticists that study the molecular structure and function of genes and how they play a role on our behavior. They find genes that allow us to have traits such as body weight, sexual orientation, and extraversion and attempt to find out which specific genes influence each of these behaviors.

  • When discussing the nature vs. nurture debate it is important to note that often both play an important role in our development and behavior. The interaction of both factors is of particular relevance to those studying epigenetics. Epigeneticists look at how the environment🌲 influences how our genes are expressed without an actual change in DNA.

    • Genetics give you a foundation of who you are but the environment shapes you into the person you are. The change between the foundation and who you really are is studied by epigeneticists.

      • These environmental changes explain why each child in a family is different, despite their same genetic background.

    • Life experiences lay down epigenetic marks, which are methyl molecules that can block the expression of a gene. Epigenetic marks are an example of changes in genes without an actual change in DNA🧬.


Image Courtesy of Myers' AP Psychology Textbook 2nd edition

"Life experiences beginning in the womb lay down epigenetic marks - often organic methyl molecules - that can block the expression of any gene in the associated DNA segment (from Champagne, 2010)."

  • Mutations are random errors that occur during gene replication that lead to a change.


  • Evolutionary psychologists focus on the principles of natural selection to explain our behavior and the mind. This principle states that we are more likely to inherit and pass along traits that have been vital to our survival as a species.

    • Charles Darwin has an large influence in this field of psychology.

The Biopsychosocial Approach

It is important to note that biological (genes)🧬, psychological (gene expression + beliefs)🧠, and social-cultural (peer influence)😊 influences all play a part in our individual development.

🎥Watch: AP Psychology - Body Systems, Brain, & Genetics

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