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 visually represent these relationships, showing how species diverge from common ancestors over time.

• Phylogenetic Tree: A diagram that represents evolutionary relationships among organisms.

• Ancestor: An organism from which others have descended.

• Speciation: The process by which one species splits into two or more separate species.

Ancestry Between Lineages

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

• Lineages can have unique histories (e.g., unique to B or C) and shared histories (e.g., B and C share a more recent ancestor than with A).

Unique vs. Common Ancestors

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

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

• For example, B and C may share a more recent common ancestor with each other than with A.

Example: In a tree with species A, B, and C, the most recent common ancestor of B and C is not the same as the common ancestor of all three.

What is Evolution and How Does it Work?

Introduction to Evolution

Evolution is the process by which populations of organisms change over generations through variations in traits, often driven by natural selection. It explains the diversity of life and the adaptation of organisms to their environments.

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

• Trait: A characteristic or feature of an organism.

Natural Selection

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

• Heritability: Some of this variation is genetic and can be passed to offspring.

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

• Change in Trait Frequency: Over generations, the frequency of beneficial traits increases in the population.

Example: In a population of beetles, those with coloration that camouflages them from predators are more likely to survive and reproduce, leading to an increase in that coloration trait over time.

Equation:

The Genetics of Color Vision

Introduction to Color Vision Genetics

Color vision in animals is determined by specific genes that code for opsin proteins, which are light-sensitive proteins found in photoreceptor cells of the eye. The presence and variation of opsin genes influence the range of colors an organism can perceive.

• Opsin Gene: A section of DNA on a chromosome that encodes an opsin protein.

• Photoreceptor: A specialized cell in the retina that detects light.

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

Example: Humans have multiple opsin genes, allowing for trichromatic color vision (perception of red, green, and blue).

Things to Remember About Selection

Key Points of Natural and Artificial Selection

Selection, whether natural or artificial, is a process that determines which individuals pass their genes to the next generation. The direction and outcome of selection depend on environmental circumstances and human intervention in the case of artificial selection.

• Only individuals that survive and reproduce can pass on their genes.

• Populations, not individuals, evolve over time.

• Selection is influenced by environmental factors, which can change and thus alter the direction of selection.

• Artificial Selection: Humans select for desired traits in organisms, such as crops or domesticated animals.

Example: Breeding dogs for specific traits like size or temperament is artificial selection.

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.

• Characteristics of populations change over time through natural selection.

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

• All species come from pre-existing species.

The Cell Theory

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

• All organisms are made up of one or more cells.

• The cell is the smallest unit of life with all the properties of living things.

• Cells arise only from the growth and division of pre-existing cells.

Example: In multicellular organisms, all cells descend from a single fertilized egg cell.

Unity of Life: Shared Characteristics Across Domains

Four Characteristics Shared by All Three Domains

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

• All are composed of cells.

• All use DNA as their genetic material.

• All carry out metabolism (chemical reactions to sustain life).

• All respond to environmental stimuli and reproduce.

Table: Comparison of the Three Domains

Additional info: The table above summarizes the unity and diversity among the three domains of life.