Bio 3-5 1

Bio Mechanisms that Produce Change in Population

EVOLUTION

  • Refers to the cumulative change in a population of organisms over time.

ARTIFICIAL SELECTION

  • Selective breeding.

  • Artificial selection: process by which humans choose individual organisms based on certain phenotypic trait values for breeding.

  • Some traits chosen may be maladaptive.

NATURAL SELECTION

  • Known as "survival of the fittest."

  • Process through which populations of living organisms adapt and change due to environmental pressures (competition, predation, climate, disease, etc.).

GENETIC DRIFT

  • Change in frequency of an existing gene variant in a population due to random chance.

  • May cause gene variants to disappear, reducing genetic variation.

Types of Genetic Drift

FOUNDER EFFECT

  • Observed when few individuals become separated from the main population (e.g., after a natural disturbance) and establish a new colony.

BOTTLENECK EFFECT

  • Occurs when the population size is drastically reduced, leaving a few surviving individuals to reproduce in a new environment.

GENE FLOW

  • Movement of alleles out of a population (emigration may reduce genetic variation) or into a population (immigration may increase gene pool diversity).

MUTATION

  • Change in the DNA sequence of an organism, can result from errors in DNA replication, exposure to mutagens, or viral infection.

RECOMBINATION

  • Occurs during meiosis when chromosomes exchange genes, leading to unique gametes and promoting genetic diversity.

Evidences of Evolution

EVIDENCES FROM FOSSILS

  • Fossils: remains of ancient organisms found in various geological settings (rocks, tar pits, ice, amber).

  • Fossil records show gradual evolutionary descent from simpler to complex life forms.

  • Example: Archaeopteryx links birds to dinosaurs.

  • Newly discovered Baminornis zhenghensis shares characteristics with modern birds.

Support for Darwin’s Findings

  • Different organisms thrived in different time periods.

  • Fossils from adjacent rock layers are more similar than those from distant layers.

  • Transitional species found between rock layers.

EVIDENCES FROM STRUCTURES

  • Homologous Structures: Organs with different functions but similar structures.

  • Analogous Structures: Perform the same function but have different embryological origins.

  • Vestigial Structures: Attributes that have lost most of their ancestral function in modern species.

EVIDENCES FROM EMBRYOLOGY

  • Studying organism development from embryo to adult stages reveals common structures that disappear in juvenile stages.

  • Vertebrates share common embryological features (e.g., pharyngeal gill slits, post-anal tail).

EVIDENCES FROM MOLECULAR BIOLOGY

  • Similar molecules of life (DNA, RNA, proteins) suggest descent from a common ancestor with modifications.

  • Cytochrome c amino acid sequence comparison provides insights into evolutionary relationships, with fewer differences indicating closer relation.

  • Example differences from humans include:

    • 0 – Chimpanzee

    • 1 – Rhesus monkey

    • 9 – Rabbit

    • 10 – Cow

    • 20 – Bullfrog

    • 42 – Yeast

EVIDENCES FROM BIOGEOGRAPHY

  • Biogeography studies the geographical distribution of fossils and living organisms.

  • Similar organisms in different locations suggest previous connections.

  • Example: Similarities between anteater and armadillo illustrate continental drift.

PHYLOGENETIC TREE

  • A diagram depicting evolutionary descent of species from a common ancestor.

  • Cladograms: branching diagrams showing ancestral relationships among organisms.

Evolution and Origin of Biodiversity: Patterns and Descents with Modification

Species Definition

  • Ernst Mayr: species are interbreeding natural populations reproductively isolated from others.

Reproductive Isolating Mechanisms

  • Prevents mating and production of fertile offspring:

    • Pre-zygotic isolation: prevents mating or fertilization (e.g., temporal, habitat, mechanical).

    • Post-zygotic isolation: affects zygotes or hybrids (e.g., zygote mortality).

Pre-zygotic Isolation

Geographic Isolation

  • Separation by physical barriers (e.g. mountains, water).

  • Example: Kaibab squirrel isolated on the Grand Canyon rim.Temporal or Seasonal Isolation

  • Differences in timing of mating prevent interbreeding.

  • Example: Rana aurora breeds earlier than Rana boylii.Behavioral Isolation

  • Different mating behaviors between groups.

  • Example: Males of superb bird-of-paradise compete for mates.Mechanical Isolation

  • Physical incompatibility of reproductive organs.

  • Example: Left- and right-coiling snails cannot mate.

Gametic Isolation

  • Gametes come into contact but fertilization does not occur due to incompatibility (e.g., giant red urchins and purple urchins).

Post-zygotic Isolation

Zygotic Mortality

  • Genetic differences result in zygotes that cannot develop properly. Hybrid Inviability

  • Hybrids may die or not reach maturity (e.g., leopons). Hybrid Sterility

  • Hybrids are viable but sterile. Hybrid Breakdown

  • First generation hybrids are viable but subsequent generations may be inviable or sterile.

Speciation

  • Occurs when a group within a species separates and develops unique characteristics.

Modes of Speciation

Geographical (Allopatric) Speciation

  • Original population divided by a barrier causing reproductive isolation.Peripatric Speciation

  • Occurs when a small population is isolated by a barrier, leading to unique development.Sympatric Speciation

  • New species form from a population without geographic isolation. Parapatric Speciation

  • Evolution at the edge of a population range where members mate with neighbors more than with those farther away.

Development of Evolutionary Thought

SCIENTIST

ARISTOTLE (350 BCE)

  • Species are essentially identical and arranged hierarchically.BUFFON (1749 AD)

  • Species change and migrate, explaining distribution. ERASMUS DARWIN (1794)

  • Proposed all species branched from a common ancestor. LAMARCK (1809)

  • Believed in inheritance of acquired traits through use and disuse.LYELL (1830)

  • Changes in nature are uniform and gradual. DARWIN & WALLACE (1859)

  • Suggested natural selection as a mechanism for evolution.

Darwin’s Theory of Evolution by Natural Selection

Major Points

  1. OVERPOPULATION

    • More offspring than available resources.

  2. STRUGGLE FOR EXISTENCE

    • Every organism struggles to survive.

  3. PRESENCE OF VARIATION

    • Variation exists within species.

  4. SURVIVAL OF THE FITTEST

    • Some variations enhance survival and reproduction.

  5. VARIATIONS CAN BE TRANSMITTED

    • Surviving organisms pass beneficial traits to offspring.