UNIT 4 BIO

What is evolution?

The process by which all organisms have changed over time.

What are the three main principles of evolution?

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?

The evolution of a new and genetically unique species.

What defines a species?

A group of organisms that can reproduce and create fertile offspring.

Why are hybrids like ligers not considered species?

Because they are usually sterile and cannot produce fertile offspring.

What are the four 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.

What are the two causes of genetic change?

Mutations (random DNA changes) and Recombination (genetic mixing during meiosis/sex).

What is an allele?

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

What are the two types of adaptations?

Physical (e.g., fur color) and Behavioral (e.g., migration patterns).

What is reproductive isolation?

When two populations can no longer interbreed and produce fertile offspring.

What’s the difference between sympatric and allopatric speciation?

1. Isolation occurs within the same habitat. 2. A group becomes isolated outside the original habitat.

What are prezygotic barriers?

Geographic Isolation, Behavioral Isolation, and Temporal Isolation.

What are postzygotic barriers?

Barriers that occur after fertilization, such as Genetic Incompatibility and Hybrid Sterility.

What does natural selection explain?

Why some organisms survive and evolve over time while others don’t.

What are Darwin's influences in developing his Theory of Natural Selection?

1. Artificial Selection 2. Malthus' Theory – Populations outgrow resources, leading to death. 3. Galapagos Observations – Animals had traits suited for niches.

What are the four 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.

What is fitness?

The ability to survive and reproduce in a specific niche.

What 4 things must organisms do to be fit in their niche?

1. Get energy/food 2. Avoid being eaten 3. Handle environmental conditions 4. Reproduce.

Does natural selection act on genotype or phenotype?

Phenotype (physical traits).

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

One gene, two alleles Multiple genes leading to a range of phenotypes.

What are the three types of natural selection?

1. Directional: Favors one extreme. 2. Disruptive: Favors both extremes. 3. Stabilizing: Favors the middle trait.

What is relative dating vs radioactive dating?

1. Based on fossil depth, 2. Uses isotopes & decay (half-life) to determine exact age.

What is a half-life?

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

What are the 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).

What’s the difference between homologous and analogous structures?

Homologous: Same structure, different function → shared ancestor; Analogous: Same function, different structure → not related.

What is a vestigial structure?

A body part that has lost its original function.

What does embryology show us about evolution?

Early embryos of vertebrates look similar, indicating common ancestry.

What’s the genetic evidence for evolution?

Shared DNA across species and similar proteins from similar amino acid sequences.

What’s the difference between macroevolution and microevolution?

Large changes over long time, Small gene changes in a population.

What is it called when one species evolves into many to fill different roles?

Divergent (Adaptive Radiation)

What is symbiosis?

A close relationship between two species that affects their evolution.

What is a gene pool?

All the genes and alleles in a population.

What is a carrier?

A person with one copy of a recessive allele who does not show the trait but can pass it on.

What’s an example of a deadly recessive allele?

Tay Sachs — destroys neurons, life expectancy ≈ 4 years.

What is genetic drift?

Random change in allele frequency in a small population.

What is the Bottleneck Effect?

A population reduced by disaster, leading to survival if fit alleles remain or extinction.

What is the Founder Effect?

A new population formed by a small group, often due to isolation.