Microevolution
3. Objectives
Define the Modern Synthesis (Combination of Natural Selection & Genetics).
Differentiate between Microevolution & Macroevolution.
Understand the Five Mechanisms of Microevolution.
Explore real-life examples of these mechanisms.
4. Modern Synthesis
Evolution debate pre-1930s:
Was evolution driven by mutation or natural selection?
Modern Synthesis (1920s-30s):
Recognized that BOTH mutation & natural selection drive evolution.
Key Concepts:
Variation is inherited.
Natural selection acts on variation.
Differential reproduction changes allele frequencies.
5. Microevolution vs. Macroevolution
Microevolution | Macroevolution |
|---|---|
Small genetic changes in a population. | Large-scale changes leading to new species. |
Alters allele frequencies. | Creates new species or groups. |
Example: Peppered Moths. | Example: Dinosaurs evolving into birds. |
6. The Five Mechanisms of Microevolution
Mutation
Non-Random Mating
Natural Selection
Gene Flow
Genetic Drift
7. Evolution = Change in Allele Frequency
Definition: Evolution occurs when the frequency of alleles changes in a population over time.
Example (Blood Type in 100 people):
50 have Type A → A allele = 50% (0.5)
40 have Type B → B allele = 40% (0.4)
10 have Type O → O allele = 10% (0.1)
📌 Key Idea: Evolution is driven by changes in allele frequencies over generations.
8. Mechanism 1: Mutation
What is a Mutation?
A spontaneous change in DNA sequence.
Mutations introduce genetic variation.
Some mutations are caused by external mutagens:
Chemicals (e.g., smoking)
Radiation (e.g., X-rays, UV light)
Effects of Mutations
Type | Impact |
|---|---|
Lethal | Causes death. |
Neutral | No effect (most common). |
Beneficial | Increases survival (rare). |
Example: Sickle Cell Mutation
Cause: A point mutation in the hemoglobin gene.
Effects:
HbS/HbS (Two copies) → Sickle Cell Anemia (severe disease).
HbA/HbS (One copy) → No disease + Malaria resistance.
HbA/HbA → Normal blood, but vulnerable to malaria.
📌 Key Idea: In malaria-prone areas, the sickle cell allele persists because it offers a survival advantage.
9. Mechanism 2: Non-Random Mating
Mating is NOT always random!
Affects genetic diversity by changing genotype frequencies.
Two Types of Non-Random Mating:
1. Assortative Mating (Similar Individuals Mate)
Decreases genetic diversity (more homozygosity).
Example:
Achondroplasia (Dwarfism): High rates of in-group pairing.
Habsburg Jaw (Royal Inbreeding): Due to royal family inbreeding.
2. Disassortative Mating (Different Individuals Mate)
Increases genetic diversity (more heterozygosity).
Example:
Redheads: Tend to mate outside their hair color group.
📌 Key Idea: Mating choice affects genetic variation.
10. Mechanism 3: Natural Selection
Definition: Favorable traits increase survival & reproduction, while unfavorable traits decrease over generations.
Modern Examples of Natural Selection
Lactose Tolerance:
A mutation in Europeans & some African populations allowed adults to digest milk.
75% of the world is still lactose intolerant!
Wisdom Teeth Evolution:
Humans evolved smaller jaws due to softer diets.
Some people never develop wisdom teeth (mutation).
📌 Key Idea: Natural selection favors traits that improve survival and reproduction.
11. Mechanism 4: Gene Flow
Definition: Exchange of genes between populations.
Occurs due to: Migration & interbreeding.
Can introduce new genetic variation to a population.
Examples of Gene Flow
Europeans & Native Americans Interbreeding.
Neanderthal DNA in Modern Humans (~1-4%).
📌 Key Idea: Gene flow increases genetic diversity & connects populations.
12. Mechanism 5: Genetic Drift
Definition: Random changes in allele frequencies.
More significant in small populations.
Types of Genetic Drift:
1. Founder Effect
A small group breaks off & forms a new population.
Example: Amish people have higher rates of genetic diseases due to intermarrying within a small founder population.
2. Bottleneck Effect
Disaster or event reduces population size.
Example: Cheetahs have low genetic diversity due to past bottleneck events.
📌 Key Idea: Genetic drift is random & can lead to reduced variation in populations.
13. Are Humans Still Evolving?
✅ Yes!
Unless we start cloning, evolution will continue.
Modern technology (e.g., genetic modification, medical advancements) influences natural selection.
📌 Key Idea: Evolution is an ongoing process!
14. Summary: Five Mechanisms of Microevolution
Mechanism | Definition | Example |
|---|---|---|
Mutation | DNA changes introducing variation | Sickle Cell Anemia |
Non-Random Mating | Selection of mates alters genotype frequencies | Assortative mating in royalty |
Natural Selection | Favorable traits increase in population | Lactose tolerance |
Gene Flow | Migration introduces new genes | European & Native American interbreeding |
Genetic Drift | Random changes in allele frequency | Founder Effect in Amish populations |