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

Understanding Phylogeny

Introduction to Phylogeny

Phylogeny is the study of the evolutionary relationships among biological species based on similarities and differences in their physical or genetic characteristics. Phylogenetic trees are diagrams that represent these relationships and help us understand the ancestry and divergence of species.

• Phylogenetic Tree: A branching diagram showing the inferred evolutionary relationships among various species or entities based on similarities and differences in their physical or genetic characteristics.

• Ancestor: An organism from which others have descended.

• Speciation: The process by which new species arise from existing ones.

Ancestry Between Lineages

• Each branch point (node) in a phylogenetic tree represents a common ancestor shared by the lineages branching from that node.

• Lineages can have unique histories (e.g., unique to species B or C) and shared histories (e.g., the common history of B and C before they diverged).

Unique vs. Common Ancestors

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

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

• Understanding these relationships helps clarify evolutionary patterns and the relatedness of species.

What is Evolution and How Does it Work?

Mechanisms of Evolution

Evolution is the process by which populations of organisms change over generations through variations in traits, often driven by natural selection. This process leads to the adaptation of organisms to their environments and the emergence of new species.

• Variation in a Population: Individuals in a population differ in their traits.

• Heritability: Some of these variations are genetic and can be passed to offspring.

• Differential Survival and Reproduction: Individuals with advantageous traits are more likely to survive and reproduce.

• Frequency of Selected Traits: Over generations, the frequency of advantageous traits increases in the population.

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

Natural Selection

• Natural selection is the process by which certain traits become more common in a population because they confer a survival or reproductive advantage.

• It acts on existing variation within a population.

• The direction of selection can change if environmental circumstances change.

Artificial Selection

• Artificial selection is the process by which humans selectively breed organisms for desired traits.

• This process is similar to natural selection but is directed by human choice rather than environmental pressures.

• Examples include breeding of crops, pets, and livestock.

The Genetics of Color Vision

Opsin Genes and Color Vision

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

• Opsin Gene: A section of DNA on a chromosome that codes for an opsin protein, which is essential for color vision.

• Photoreceptor: A specialized cell in the retina that responds to light and enables vision.

• Gene to Function: The flow of genetic information can be summarized as: GENE → PROTEIN → FUNCTIONAL UNIT (PHOTORECEPTOR) → CELL → ORGANISM

Example

• Mutations in opsin genes can lead to color vision deficiencies, such as red-green color blindness in humans.

Major Unifying Concepts of Biology

Theory of Evolution by Natural Selection

The theory of evolution by natural selection is a central concept in biology, explaining how populations change over time and how all species are related by descent from common ancestors.

• Pattern: Characteristics of a population change over time.

• Mechanism: Evolution occurs through natural selection.

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

Cell Theory

Cell theory is another foundational concept in biology, stating that all living organisms are composed of cells, and all cells arise from pre-existing cells.

• All organisms are made up of cells.

• The cell is the smallest unit of life.

• All cells arise from the division of pre-existing cells.

Unity and Diversity of Life: The Three Domains

Shared Characteristics of All Cells

Despite the diversity of life, all cells share certain fundamental characteristics, reflecting the unity of life across the three domains: Bacteria, Archaea, and Eukarya.

• Plasma Membrane: All cells are surrounded by a plasma membrane that controls the movement of substances in and out of the cell.

• Genetic Material: All cells contain DNA as their genetic material.

• Ribosomes: All cells have ribosomes for protein synthesis.

• Cytoplasm: All cells contain cytoplasm, the semi-fluid substance inside the cell membrane.

Comparison of the Three Domains

The three domains of life—Bacteria, Archaea, and Eukarya—share these core cellular features but differ in other structural and genetic characteristics.

Characteristic	Bacteria	Archaea	Eukarya
Cell Type	Prokaryotic	Prokaryotic	Eukaryotic
Membrane-bound Organelles	No	No	Yes
Cell Wall Composition	Peptidoglycan	Varied (no peptidoglycan)	Varied (cellulose, chitin, or none)
Examples	Escherichia coli	Halobacterium	Homo sapiens, Arabidopsis thaliana

Unity: The shared cellular features among all domains highlight the unity of life, while differences account for the diversity observed among organisms.

Additional info: The table above is inferred from standard biology knowledge, as the original table was not fully visible.