BackGenes, Environment, and Heritability: Foundations for Psychology
Study Guide - Smart Notes
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Genes and Environment
Introduction to Genetics
Understanding genetics is fundamental to exploring how biological factors influence psychological traits and behaviors. This section introduces the basic units of genetic material and their organization.
Genes: Biological units of heredity passed from parents to offspring, composed of segments of DNA.
DNA: The molecule that holds genetic information, organized into chromosomes.
Chromosomes: Thread-like structures that organize and package DNA; humans have 23 pairs of chromosomes.
Example: The organization of genetic material can be summarized as: genes → DNA → chromosomes
Smallest Unit | Intermediate | Largest Unit |
|---|---|---|
Genes | DNA | Chromosomes |
Genotype and Phenotype
When studying genetics, psychologists distinguish between genotype and phenotype:
Genotype: The genetic makeup of an organism; the set of genes it carries.
Phenotype: Observable characteristics, including physical qualities, mental qualities, and behavior.
Most traits are polygenic, meaning they are influenced by more than one gene.
Phenotypes result from the interaction of genes and environment.
Example: Eye color is a phenotype determined by multiple genes (genotype) and can be influenced by environmental factors.
Heredity
Heritability
Heritability measures how much variation in phenotype across people is due to differences in genotype. It is calculated as a proportion from 0 to 1, called a heritability estimate.
Heritability Estimate:
Genes do not contribute to all differences in traits.
In research, where only genes contribute, heritability typically ranges from 0 (not at all) to 1 (totally).
Studying Heritability: Twin Studies
Psychologists often study heritability by comparing twins:
Monozygotic (Identical) Twins: Share 100% of their genetic material.
Dizygotic (Fraternal) Twins: Share about 50% of their genetic material.
Type of Twin | Genetic Similarity |
|---|---|
Monozygotic (Identical) | 100% |
Dizygotic (Fraternal) | 50% |
Example: Twin studies help researchers separate genetic influences from environmental ones by comparing similarities between identical and fraternal twins.
Why Are Twin Studies Useful in Psychology?
They allow researchers to "control" for genetics or the environment.
They help researchers test traits in many subjects.
They allow researchers to have an experimental group.
Notes About Heritability
Important Considerations
When interpreting heritability, it is important to remember:
We are usually not identifying specific genes that contribute to a trait.
Heritability is a population-level concept; it refers to variation within a population, not an individual.
Traits such as depression can be influenced by the environment, interventions, therapy, etc.
Example: The statement "His mother was an alcoholic, so he probably inherited the genes and will be one too" is incorrect because:
Many traits, including those involving complex behaviors, are polygenic.
Heritability refers to variation within a population, not to individuals.
Environmental factors can influence traits such as depression.
Additional info: Heritability does not imply immutability; environmental interventions can alter the expression of genetic traits.
