Foundations of Evolution, Phylogeny, and Cell Theory in General Biology

Understanding Phylogeny

Introduction to Phylogeny

Phylogeny is the study of evolutionary relationships among biological species based on similarities and differences in genetic or physical characteristics. Phylogenetic trees visually represent these relationships, showing how species diverge from common ancestors over time.

• Phylogenetic Tree: A diagram that depicts evolutionary relationships among groups of organisms.

• Ancestor: An organism from which others have descended.

• Speciation: The process by which new species arise.

Ancestry Between Lineages

Lineages can be traced back to their ancestors, revealing unique and shared evolutionary histories. The branching points (nodes) on a phylogenetic tree represent common ancestors.

• Unique History: Each lineage has a portion of its history that is not shared with others.

• Shared History: Lineages may share a common ancestor, indicating a shared evolutionary path.

Unique vs Common Ancestors

Phylogenetic trees help distinguish between unique ancestors (specific to one lineage) and common ancestors (shared by multiple lineages).

• Unique Ancestor: An ancestor specific to a single lineage.

• Common Ancestor: An ancestor shared by two or more lineages.

• Application: Understanding ancestry helps clarify evolutionary relationships and classification.

Evolution and Natural Selection

What is Evolution?

Evolution is the process by which populations of organisms change over generations through variations in traits. These changes are driven by mechanisms such as natural selection.

• Definition: Evolution is a change in the heritable traits of a population over time.

• Population: A group of individuals of the same species living in a specific area.

Mechanism of Natural Selection

Natural selection is the primary mechanism of evolution, where individuals with advantageous traits are more likely to survive and reproduce.

• Variation in Population: Individuals differ in their traits.

• Heritability: Variation must be genetically inherited.

• Differential Survival & Reproduction: Individuals with beneficial traits survive and reproduce more successfully.

• Frequency of Selected Traits: Beneficial traits become more common in subsequent generations.

Equation:

$\text{Evolutionary Change} = \text{Change in Trait Frequency Over Time}$

Key Points about Selection

• Survival to Reproduction: Only individuals that survive to reproduce pass on their genes.

• Population Evolution: Populations, not individuals, evolve over time.

• Selection Direction: The direction of selection can change as environmental circumstances change.

Artificial Selection

Artificial selection is a process where humans selectively breed organisms for desired traits, contrasting with natural selection driven by environmental pressures.

• Definition: Artificial selection is the intentional breeding of organisms by humans.

• Example: Breeding dogs for specific traits such as size or temperament.

The Genetics of Color Vision

Opsin Genes and Color Vision

Color vision in organisms is determined by opsin proteins, which are encoded by specific sections of DNA called opsin genes. These genes are located on chromosomes and are responsible for the production of photoreceptor proteins in the eye.

• Opsin Gene: A segment of DNA that codes for an opsin protein.

• Photoreceptor: A cell in the retina that detects light and enables vision.

• Gene to Organism Pathway: GENE → PROTEIN → FUNCTIONAL UNIT (PHOTORECEPTOR) → CELL → ORGANISM

• Application: Mutations in opsin genes can lead to color vision deficiencies.

Major Unifying Concepts of Biology

The Theory of Evolution

The theory of evolution by natural selection explains how populations change over time and how all species are related by descent from common ancestors.

• Population Change: Characteristics of populations change over time.

• Mechanism: Evolution occurs through natural selection.

• Common Descent: All species are related by descent from a common ancestor.

The Cell Theory

The cell theory is a fundamental concept in biology stating that all living organisms are composed of cells, and all cells arise from pre-existing cells.

• Pattern: All organisms are made up of cells.

• Mechanism: All cells come from pre-existing cells.

• Application: In multicellular organisms, all cells descend from an ancestral cell.

Unity Among the Three Domains of Life

Shared Cellular Characteristics

Despite their diversity, organisms in the three domains of life—Bacteria, Archaea, and Eukarya—share fundamental cellular characteristics, reflecting the unity of life.

• Four Shared Characteristics:

  1. All are composed of cells.

  2. All use DNA as genetic material.

  3. All carry out metabolism.

  4. All respond to environmental stimuli.

• Domains of Life:

  • Bacteria: Prokaryotic, unicellular organisms.

  • Archaea: Prokaryotic, often extremophiles.

  • Eukarya: Eukaryotic, includes unicellular and multicellular organisms.

Comparison Table: Domains of Life

The following table summarizes key differences and similarities among the three domains:

Domain	Cell Type	Genetic Material	Metabolism	Environment
Bacteria	Prokaryotic	DNA	Varied	Ubiquitous
Archaea	Prokaryotic	DNA	Varied	Often extreme
Eukarya	Eukaryotic	DNA	Varied	Varied

Additional info: The four shared characteristics are inferred from standard biology curriculum, as the original notes were fragmented.