AP Biology 5.5 Environmental Effects on Phenotype Study Notes - New Syllabus Effective 2025
AP Biology 5.5 Environmental Effects on Phenotype Study Notes- New syllabus
AP Biology 5.5 Environmental Effects on Phenotype Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Explain how the same genotype can result in multiple phenotypes under different environmental conditions.
Key Concepts:
- Environmental Factors & Phenotype
5.5.A – Environmental Influence on Phenotype
🧠 What Is the Genotype and Phenotype? 
| Term | Meaning | Example |
|---|---|---|
| Genotype | The genetic code (your alleles) | e.g. Aa or BB |
| Phenotype | The visible traits (what we see) | e.g. eye color, height, behavior |
🧬 Your genotype stays the same, but your phenotype can change depending on your environment.
🌦️ Environmental Factors That Affect Phenotype
| Environmental Factor | How It Can Change Phenotype |
|---|---|
| Temperature | Affects pigment production, enzyme activity |
| Nutrition | Influences growth, height, brain development |
| Sunlight | Affects skin color (melanin), photosynthesis in plants |
| Altitude | Changes lung capacity, red blood cell count |
| pH of soil or water | Influences flower color or plant enzyme function |
| Stress or lifestyle | Can affect hormone levels, behavior, even disease susceptibility |
🔍 Key Concept: Phenotypic Plasticity
🧠 This means the ability of an organism to change its phenotype in response to the environment – even if the genotype doesn’t change.
🧬 Phenotypic plasticity = same DNA, different expression based on environment.
🌸 Real-Life Examples
| Example | Explanation |
|---|---|
| Himalayan Rabbit | Has white fur on warm areas, black fur on cooler extremities |
| Hydrangea flowers | Blue in acidic soil, pink in neutral soil |
| Identical twins | Same DNA, but may have different heights or weights depending on nutrition |
| Malnourished child | May have same “tall” genotype, but poor diet stunts growth |
| Caterpillar form in seasons | Same species, different look depending on season (camouflage adaptation) |
⚖️ Summary:
- Genes = potential, but the environment = influence
- One genotype can lead to multiple phenotypes
- Phenotypic plasticity shows how flexible biology can be
- Helps organisms adapt and survive in different conditions
✅ Why It Matters?
This shows that not all traits are “hardwired.” For evolution, it means natural selection acts on phenotypes, which can shift due to environmental context.
5.5.A.1 – How the Same Genotype Can Lead to Different Phenotypes ?
🧬 Even if two individuals share the exact same DNA, they can look or behave differently depending on what’s happening around them. That’s where environmental influence comes in.
🌱 Phenotypic Plasticity
A single genotype (genetic makeup) can produce different phenotypes (observable traits) when the environment changes.
🌡️ How does it happen?
Think of genes like instructions, and the environment like the conditions you’re working in. The instructions stay the same, but how you carry them out can change based on temperature, diet, chemicals, sunlight, etc.
🧪 Gene activity is flexible — some genes get turned on/off or change how strongly they work depending on what’s happening around the organism.
🎯 Real-Life Examples
| Example | What Changes | Why It Happens |
|---|---|---|
| Fish in warm vs. cold water | Body size and growth rate | Cold temps slow metabolism → slower growth |
| Maple tree leaves | Leaf color in fall | Cooler temps + less light = changes in pigment gene expression |
| Snakes’ skin patterns | Color and pattern | Soil and sunlight affect skin cell development |
| Human metabolism | Fat storage and energy use | Long-term diet and lifestyle affect how metabolism genes are expressed |
| Insects like locusts | Solitary vs. swarming behavior | Crowded environments turn on genes for swarming! |
🎓 Key Idea
Our DNA isn’t a fixed destiny – how your body uses your DNA can shift based on where you live, what you eat, the climate, or even stress levels.
📘Keywords:
| 📌 Term | 💬 Meaning |
|---|---|
| Phenotype | The way an organism looks or acts |
| Genotype | The actual DNA code (alleles) an organism has |
| Phenotypic Plasticity | One set of genes creating different outcomes based on the environment |
| Gene expression | Turning genes “on” or “off” — or changing how active they are |
🧩 Why it’s important:
- Helps organisms adapt to changing environments
- Shows that traits are influenced by both genes and environment
- Helps explain evolutionary success and survival strategies