Evolutionary Concepts

Natural Selection

Natural selection is the process by which organisms better adapted to their environment tend to survive and produce more offspring. This mechanism drives evolutionary change.

• Definition: Differential survival and reproduction of individuals due to differences in phenotype.

• Key Point: Acts on heritable traits that affect fitness.

• Example: Peppered moths in industrial England.

Fitness

Fitness refers to an organism's ability to survive and reproduce in its environment.

• Definition: The reproductive success of an individual relative to others in the population.

• Key Point: Higher fitness means more offspring are produced.

Population

A population is a group of individuals of the same species living in a specific area.

• Key Point: Populations are the units of evolution.

Homologies vs. Analogies

Homologies and analogies describe similarities between organisms.

• Homology: Similarity due to shared ancestry (e.g., vertebrate forelimbs).

• Analogy: Similarity due to convergent evolution, not common ancestry (e.g., wings of birds and insects).

Convergent Evolution

Convergent evolution occurs when unrelated species evolve similar traits independently.

• Example: Dolphins and sharks both have streamlined bodies for swimming.

Gene Pool and Alleles

The gene pool is the total collection of genes in a population. Alleles are different forms of a gene.

• Gene Pool: All alleles present in a population.

• Allele: Variant form of a gene (e.g., A and a).

Mechanisms of Evolution

Evolution occurs through several mechanisms that change allele frequencies in populations.

• Natural Selection: See above.

• Mutations: Random changes in DNA that introduce new alleles.

• Genetic Drift: Random changes in allele frequencies, especially in small populations.

  • Bottleneck Effect: Sharp reduction in population size, reducing genetic diversity.

  • Founder Effect: New population started by a few individuals, leading to different allele frequencies.

• Gene Flow: Movement of alleles between populations via migration.

• Sexual Selection: Selection for traits that increase mating success.

Speciation and Reproductive Barriers

Speciation is the formation of new species, often through reproductive isolation.

• Prezygotic Barriers: Prevent mating or fertilization.

  • Habitat Isolation: Species live in different environments.

  • Behavioral Isolation: Different mating behaviors.

  • Mechanical Isolation: Physical incompatibility of reproductive organs.

  • Temporal Isolation: Different mating times.

  • Gametic Isolation: Gametes cannot fuse.

• Postzygotic Barriers: Affect hybrid offspring.

  • Hybrid Fertility: Hybrids are sterile.

  • Hybrid Breakdown: Hybrids are viable but their offspring are weak or sterile.

• Allopatric Speciation: Speciation due to geographic isolation.

• Sympatric Speciation: Speciation without geographic isolation.

Population Genetics

Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium describes a non-evolving population where allele and genotype frequencies remain constant.

• Equation:

• p: Frequency of dominant allele

• q: Frequency of recessive allele

• Assumptions: No mutation, migration, selection, or genetic drift; random mating.

Calculating Allele, Genotype, and Phenotype Frequencies

Population genetics involves calculating the frequencies of alleles, genotypes, and phenotypes.

• Allele Frequency: Proportion of a specific allele in the population.

• Genotype Frequency: Proportion of a specific genotype.

• Phenotype Frequency: Proportion of individuals with a specific trait.

• Example Calculation: If 16% of a population shows the recessive phenotype, , so and .

Bacteria

Characteristics of All Cells

Cells are the basic units of life, with common features such as a plasma membrane, cytoplasm, and genetic material.

• Prokaryotes: Cells without a nucleus (e.g., bacteria).

• Eukaryotes: Cells with a nucleus (e.g., plants, animals).

Bacterial Cell Shapes

Bacteria have characteristic shapes that aid in identification.

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillum: Spiral-shaped

Gram Positive vs. Gram Negative Bacteria

Gram staining differentiates bacteria based on cell wall structure.

• Gram Positive: Thick peptidoglycan layer; stains purple.

• Gram Negative: Thin peptidoglycan layer and outer membrane; stains pink.

Importance of Gram Staining

Gram staining is crucial for bacterial classification and guiding antibiotic treatment.

Using DNA to Identify Bacterial Species

DNA sequencing allows precise identification and classification of bacteria.

Protists

General Characteristics of Protists

Protists are a diverse group of mostly unicellular eukaryotes.

• Key Point: Protists can be autotrophic, heterotrophic, or mixotrophic.

• Nutritional Diversity: Protists obtain energy through photosynthesis, ingestion, or absorption.

Major Groups of Protists

Protists are classified into several major groups based on evolutionary relationships.

Plants

Shared Characteristics of Plants and Green Algae

Plants and green algae share several key features due to common ancestry.

• Chlorophyll a and b

• Cellulose cell walls

• Starch as storage molecule

Unique Characteristics of Plants

Plants have adaptations for terrestrial life.

• Cuticle: Waxy covering to prevent water loss

• Multicellular dependent embryos

• Alternation of generations

Alternation of Generations

Plants alternate between multicellular haploid (gametophyte) and diploid (sporophyte) stages.

• Spores: Produced by meiosis in sporophyte

• Gametes: Produced by mitosis in gametophyte

Bryophytes

Bryophytes are nonvascular plants such as mosses, liverworts, and hornworts.

• Characteristics: Lack vascular tissue, dominant gametophyte stage, require water for fertilization

• Examples: Mosses, Liverworts, Hornworts

Seedless Vascular Plants

Seedless vascular plants have vascular tissue but reproduce via spores.

• Characteristics: Dominant sporophyte stage, vascular tissue (xylem and phloem)

• Examples: Ferns, Club mosses

Seed Plants

Seed plants include gymnosperms and angiosperms, characterized by seeds and pollen.

• Characteristics: Seeds, pollen, reduced gametophyte, dominant sporophyte

Evolutionary Importance of Seeds and Fruits

The development of seeds and fruits was a major evolutionary step for plants.

• Seeds: Protect and nourish the embryo, allow dormancy and dispersal

• Fruits: Aid in seed dispersal, attract animals

Angiosperms

Angiosperms are flowering plants with unique adaptations.

• Unique Characteristics: Flowers, fruits, double fertilization

• Importance: Flowers attract pollinators; fruits aid in seed dispersal