UNIT 4 BIO

SECTION 4-1: SPECIATION

💡 What is Evolution?

Q: What is evolution? A: The process by which all organisms have changed over time.

🔑 3 Main Principles of Evolution

Q: What are the three main principles of evolution? A:

1. All organisms share common descent from unicellular ancestors.

2. Organisms have diversified over time into many forms with different traits.

3. Natural selection is the mechanism behind evolutionary change.

🧬 What is Speciation?

Q: What is speciation? A: The evolution of a new and genetically unique species.

👶 Definition of Species

Q: What defines a species? A: A group of organisms that can reproduce and create fertile offspring.

Q: Why are hybrids like ligers not considered species? A: Because they are usually sterile and cannot produce fertile offspring.

🪜 4 Steps of Speciation

1. Genetic Change: Random mutations or recombination

2. Variations: Differences in phenotypes

3. Adaptations: Inherited traits that improve survival

4. Reproductive Isolation: Leads to a new species

🧪 Types of Genetic Change

Q: What are the two causes of genetic change? A:

• Mutations (random DNA changes)

• Recombination (genetic mixing during meiosis/sex)

🧬 What is an Allele?

A: A version of a gene. Each gene may have multiple alleles.

🔄 Types of Adaptations

Q: What are the two types of adaptations? A:

• Physical (e.g., fur color)

• Behavioral (e.g., migration patterns)

🧱 Reproductive Isolation

Q: What is reproductive isolation? A: When two populations can no longer interbreed and produce fertile offspring.

🌍 Types of Speciation

Q: What’s the difference between sympatric and allopatric speciation? A:

• Sympatric: Isolation occurs within the same habitat.

• Allopatric: A group becomes isolated outside the original habitat.

🚫 Prezygotic Barriers (before zygote)

1. Geographic Isolation: Physical separation (deserts, oceans, mountains) 2. Behavioral Isolation: Different mating behaviors 3. Temporal Isolation: Reproduce at different times

❌ Postzygotic Barriers

1. Genetic Incompatibility 2. Hybrid Sterility

SECTION 4-2: NATURAL SELECTION

🌿 Darwin’s Theory of Natural Selection

Q: What does natural selection explain? A: Why some organisms survive and evolve over time while others don’t.

🔍 Darwin’s Influences

1. Artificial Selection

2. Malthus' Theory – Populations outgrow resources, leading to death.

3. Galapagos Observations – Animals had traits suited for niches.

⚙ 4 Key Ideas of Natural Selection

1. Variations exist within populations.

2. Some variations increase fitness.

3. Not all offspring survive (competition).

4. Survivors reproduce and pass on traits.

🧩 Fitness & Niche

Q: What is fitness? A: The ability to survive and reproduce in a specific niche.

Q: What 4 things must organisms do to be fit in their niche?** A:

1. Get energy/food

2. Avoid being eaten

3. Handle environmental conditions

4. Reproduce

🧬 Natural Selection Acts On…

Q: Does natural selection act on genotype or phenotype? A: Phenotype (physical traits).

Single-Gene vs. Polygenic Traits

Q: What’s the difference between single-gene and polygenic traits? A:

• Single-Gene Trait: One gene, two alleles. One trait selected.

• Polygenic Trait: Multiple genes. Range of phenotypes.

🎯 3 Types of Natural Selection

1. Directional: Favors one extreme

2. Disruptive: Favors both extremes

3. Stabilizing: Favors the middle trait

SECTION 4-3: EVIDENCE FOR EVOLUTION

🦴 Fossil Evidence

Q: What is relative dating vs radioactive dating? A:

• Relative Dating: Based on fossil depth

• Radioactive Dating: Uses isotopes & decay (half-life) to determine exact age

⏳ What is a Half-Life?

A: The time it takes for half of a radioactive sample to decay.

🌎 Major Mass Extinctions

1. Permian: 95% marine species gone (250 mya)

2. Cretaceous: Asteroid kills dinos (65 mya)

3. Pleistocene: Ice Age + humans (11 tya)

🧍‍♂ Comparative Anatomy

Q: What’s the difference between homologous and analogous structures? A:

• Homologous: Same structure, different function → shared ancestor

• Analogous: Same function, different structure → not related

Q: What is a vestigial structure? A: A body part that has lost its original function.

🐣 Embryology

Q: What does embryology show us about evolution? A: Early embryos of vertebrates look similar → common ancestry

🧬 Genetic Evidence

Q: What’s the genetic evidence for evolution? A:

• Shared DNA across species

• Similar proteins from similar amino acid sequences

• Humans & chimps share 99.8% of DNA

SECTION 4-4: EVOLUTION PATTERNS & PROCESSES

🧠 Macroevolution vs Microevolution

Q: What’s the difference? A:

• Macroevolution: Large changes over long time

• Microevolution: Small gene changes in a population

🧬 3 Patterns of Evolution

1. Divergent (Adaptive Radiation): One ancestor → many niches

   • Evidence: Homologous structures, DNA

2. Convergent: Unrelated organisms evolve similar traits

   • Evidence: Analogous structures

3. Coevolution: Two species evolve in response to each other

   • Examples: pollinators, predator-prey, mimicry, symbiosis

🤝 What is Symbiosis?

A: A close relationship between two species that affects their evolution.

🧬 Gene Pools & Allele Frequencies

Q: What is a gene pool? A: All the genes and alleles in a population.

Q: What is a carrier?** A: A person with one copy of a recessive allele who does not show the trait but can pass it on.

Q: What’s an example of a deadly recessive allele? A: Tay Sachs — destroys neurons, life expectancy ≈ 4 years

🎲 Genetic Drift

Q: What is genetic drift? A: Random change in allele frequency in a small population

🔥 Bottleneck Effect vs Founder Effect

• Bottleneck: Population reduced by disaster

  • Outcomes: Survive if fit alleles remain OR go extinct

• Founder Effect: New population formed by a small group (usually via isolation)

Q: What is it called when one species evolves into many to fill different roles?
A: Divergent (Adaptive Radiation)

Q: What describes unrelated species developing similar features due to similar environments?
A: Convergent evolution

Q: What is it when two species change over time in response to each other?
A: Coevolution