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IB DP Psychology — Biological Approach | SL & HL | Paper 1
🎯 Learning Intentions By the end of this note, you will be able to:
- Define genetic inheritance, genotype, phenotype, and heritability using IB-aligned terminology.
- Explain how genes influence behaviour through the relationship between genotype and phenotype.
- Describe the logic and methodology of twin studies and how they are used to estimate genetic contributions to behaviour.
- Evaluate research evidence for genetic influences on behaviour using supporting and opposing studies in ACAS format.
- Apply concepts of genetic inheritance to a real-world case study from the biological perspective.
- Discuss the extent to which genetic inheritance provides a complete explanation of human behaviour, including the role of gene–environment interaction.
- Analyse research on genetic inheritance using relevant concept areas: Causality, Bias, Perspective, and Responsibility.
Introduction & Context
Have you ever been told you have your mother's temper, your grandfather's stubbornness, or your father's tendency to worry? These observations — made casually around dinner tables and family gatherings — point to something psychologists have investigated rigorously for over a century: the possibility that our personalities, our emotional tendencies, and even our vulnerabilities to certain mental states might be passed down through families, just as eye colour or height is. The question is not simply whether families share traits, but whether those shared traits are the result of shared genes, shared environments, or some combination of both.
This question sits at the heart of the biological approach to psychology. If behaviour has a genetic basis, then understanding inheritance becomes essential to understanding why people think, feel, and act the way they do. But genes are not destiny — they interact with the world around us in complex ways. To understand genetic influences on behaviour, we need to understand what genes actually are, how they are passed from parent to child, and what the evidence tells us about the degree to which they shape who we become.
🔍 Analogy — The Blueprint and the Building Think of your genetic code as an architectural blueprint. The blueprint contains instructions for how a building could be constructed — but the final building also depends on the materials available, the skill of the builders, and the conditions during construction. Two buildings from the same blueprint can look quite different depending on those environmental factors. In the same way, your genes provide a set of instructions for development, but the environment shapes how — and how fully — those instructions are expressed. The blueprint matters enormously, but it does not determine the outcome alone.
Core Concepts
To understand how genes influence behaviour, we first need to understand what genes are and how they are transmitted from one generation to the next. Every cell in the human body contains DNA — a long molecule that carries the instructions for building and running the organism. This DNA is organised into units called genes, and humans have approximately 20,000–25,000 of them. These genes are arranged along structures called chromosomes, and humans typically have 23 pairs of chromosomes — one set inherited from each biological parent. This means that every person carries two copies of most genes, one from each parent.
📖 Key Definition — Genetic Inheritance Genetic inheritance refers to the process by which genetic information (DNA) is transmitted from biological parents to their offspring. Each parent contributes half of the offspring's genetic material, meaning that the child's genetic makeup is a unique