Unit 2_Biodiversity and Evolution Flashcards

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Scientific Explanations for the Origin of DNA

  • Historical Context: DNA likely emerged from RNA, though the exact mechanism remains undiscovered.

  • Competing Hypotheses:

    • RNA World Hypothesis: Suggests RNA was the first self-replicating molecule and DNA evolved from it later.

    • DNA and RNA Coevolution: Suggests both molecules evolved simultaneously.

    • Ancestral Hybrid Nucleic Acid: Suggests an original molecule with characteristics of both evolved into separate DNA and RNA molecules.

  • Comparative Characteristics of DNA and RNA:

    • Stability: RNA is less stable than DNA.

    • Functional Roles: RNA acts to form proteins and store genetic information; DNA is specialized solely for storing genetic information.

    • Organismal Complexity:

      • Simple organisms are more likely to rely strictly on RNA for genetic information.

      • Complex organisms utilize DNA for storage while maintaining RNA for protein production.

The RNA World Hypothesis

  • Status: Currently the most widely accepted scientific hypothesis regarding the origin of genetic material.

  • Primary Assumptions:

    • RNA preceded DNA in the evolutionary timeline.

    • DNA eventually evolved from an RNA precursor.

  • Supporting Evidence: DNA's superior stability led to it becoming the primary method for long-term genetic storage.

  • Mechanisms of RNA Formation:

    • Hydrothermal Vents: Hypothesizes that life and RNA first evolved at hydrothermal vents located on the ocean floor.

    • Primordial Soup and Lightning: Proposes that Earth's early atmosphere contained the chemical building blocks for RNA, and lightning provided the energy to trigger the reactions necessary to create it.

    • Miller-Urey Experiment: A landmark lab study that recreated early Earth's atmospheric conditions, proving that the organic molecules necessary for life could be synthesized in such an environment.

Coevolution and Ancestral Hybrid Hypotheses

  • Coevolution Hypothesis:

    • Posits that DNA and RNA evolved at the same time within hydrothermal vents or the "primordial soup."

    • Both molecules served unique and specific roles from their inception.

  • Ancestral Hybrid Nucleic Acid Hypothesis:

    • Proposes an ancestral molecule, neither DNA nor RNA, possessed traits of both.

    • Over time, this molecule diverged into the specialized DNA and RNA molecules we see today, a process likened to molecular speciation.

    • Experimental data indicates that molecules composed of both DNA and RNA components have existed.

Support for Evolution: Common Ancestry and LUCA

  • Definition of Evolution: Scientists define evolution as the cumulative change within a group of organisms over a period of time.

  • Common Ancestry Theory: The scientific theory that all life forms descend from a single progenitor.

  • L.U.C.A.: Acronym for the "Last Universal Common Ancestor."

  • Primary Categories of Evidence:

    • 1. The Fossil Record.

    • 2. Biogeography (Geographic distribution and isolation).

    • 3. Homologies:

      • Anatomical: Homologous structures.

      • Molecular: Comparative biochemistry.

      • Developmental: Comparative embryology.

The Fossil Record and the Law of Superposition

  • The Fossil Record: A comprehensive collection of all fossils discovered on Earth that provides a chronological history of life.

  • Dating Principles:

    • Fossils are generally assumed to be the same age as the rock layer (stratum) in which they are discovered.

    • Species found in the same rock layer are assumed to have coexisted at the same time.

  • Law of Superposition:

    • Bottom rock layers are the oldest.

    • Higher rock layers are younger.

    • This principle allows scientists to date fossils across different geographical regions.

  • Evolutionary Example (Horses): Modern horses differ significantly from their ancestors; fossil records provide evidence of shared ancestry through skeletal similarities.

Clues of Evolution in the Fossil Record: Stasis and Change

  • Stasis: A period where a species undergoes little to no evolutionary change.

  • Punctuated Equilibrium:

    • Characterized by long periods of stasis followed by a sudden shift or rapid change.

    • Often triggered by environmental shifts selecting for new dominant traits.

    • Example: A species of mollusk maintained a consistent shell shape for a long period before a sudden environmental change led to younger fossils displaying an elongated shell. This typically lacks transitional fossils.

  • Gradualism:

    • Evolution occurring at a slow, constant pace.

    • Example: The camel evolved larger skulls and longer limb bones gradually over a long period due to environmental pressures.

    • Transitional Fossils: Fossils that document the small, intermediate changes as one species evolves into another; these are common in gradualism.

Geographic Distribution and Isolation (Biogeography)

  • Geographic Distribution: Closely related species are typically found in geographical proximity to one another.

    • Example: Butterflies in South America are more closely related to other South American species than they are to those in Australia.

  • Geographic Isolation: Occurs when two populations are separated by physical barriers such as rivers, mountains, or bodies of water.

  • Speciation: The formation of barriers can lead to the development of new species.

    • Example (Pork Fish): A gap between North and South America closed 3.53.5 billion years ago (per transcript), connecting the land and causing the development of two distinct Pork fish species.

  • Relationship Inference: Species separated by massive geographic barriers are unlikely to share a recent common ancestor.

Comparative Anatomy: Homologous, Analogous, and Vestigial Structures

  • Homologous Structures:

    • Anatomically similar structures inherited from a common ancestor.

    • These structures have different functions in different species despite having similar bone structures (e.g., limbs of various mammals).

  • Analogous Structures:

    • Structures that serve the same function but are anatomically different.

    • Example: Bat wings and insect wings both facilitate flight, but bats have bones while insects do not.

    • Significance: Analogous structures do not indicate common ancestry.

  • Vestigial Structures:

    • Reduced versions of functional structures that no longer serve a purpose in a modern organism.

    • Used by scientists to determine ancestral lineages.

Developmental-Comparative Embryology

  • Premise: Closely related organisms exhibit physical similarities during their embryonic development before birth.

  • Developmental Progression: In humans and other mammals, development follows a similar progression.

  • Shared Embryonic Traits: In their early stages, embryos of fish, turtles, chickens, and humans all possess:

    • A notochord.

    • A hollow dorsal nerve cord.

    • Pharyngeal gill slits.

    • Post-anal tails.

  • Relatedness: The more closely related two organisms are, the longer they maintain similar appearances during later stages of embryonic development.

Molecular Comparative Biochemistry

  • Biochemical Similarity: The degree of relatedness between species corresponds to the similarities in their biochemistry.

  • Molecular Evidence: Related organisms share more nitrogen bases in their DNA and similar amino acid sequences in their proteins.

  • Key Principle: Higher similarities in DNA sequences generally result in more similar amino acid chains, suggesting closer relatedness.

Diagrams Representing Evolutionary Relationships

  • Cladograms: Charts listing related organisms that depict the successive points of species divergence from common ancestral lines.

  • Dendrograms: Branching diagrams representing a hierarchy of categories based on shared characteristics or degrees of similarity over time.

  • Timelines: Chronological arrangements of biotic and abiotic events in the order they occurred.

  • Spindle Diagrams: Illustrate taxonomic diversity within geologic time.

    • Width of the "spindle" indicates the number of families or diversity level.

    • When a group no longer extends upward on the diagram, it indicates extinction.

    • Example Observations: Ray-fin fishes and spiny sharks coexisted. Spiny sharks had more diversity in the Devonian and Carboniferous periods than Ray-fin fishes. Tetrapods share a more recent common ancestor with lobe-fin fishes than with other groups.

Questions & Discussion

  • Fossil Record Practice:

    • Question 1: Which fossil (W, X, or Y) is the youngest? Why?

    • Question 2: Which layer of the earth is the oldest? Why?

    • Question 3: What do you notice about fossils as we move through time?

  • Method of Evolution Practice:

    • Question 1: What does Image A (Gradualism) indicate and why?

    • Question 2: What does Image B (Punctuated Equilibrium) indicate and why?

    • Question 3: What would you expect to see in the fossil record of an organism that went through gradualism?

    • Question 4: What could cause the rapid change observed in punctuated equilibrium? Options: A) Stable environment, B) No competition, C) Sudden environmental changes, D) Lack of mutations.

    • Question 5: In the model of __________, evolutionary changes happen slowly and continuously over a long period.

    • Question 6: __________ equilibrium suggests most species stay the same for long times, with rapid changes happening in short bursts.

    • Question 7: A period of little or no evolution: __________.

  • Geographic Distribution Practice:

    • Question 1: What do the red lines represent on the lizard distribution diagram?

    • Question 2: Why do the lizards in the dotted circle look similar?

    • Question 3: Monkeys in Africa are different species from the same ancestor; what might have caused them to evolve over time?

  • Homologous Structures and Embryology Practice:

    • Question 1: Which two are most closely related: Bird, Bat, or Insect?

    • Question 2: How do you know?

    • Question 3: True/False: We can tell how closely related two species are by comparing homologous structures NOT their function.

    • Question 4: What is noticeable about all embryos at Stage 1?

    • Question 5: What can be concluded about their ancestry based on embryonic images?

    • Question 6: Which organism is least closely related to the human at Stage 2?

  • Molecular Biochemistry Practice:

    • Question 1: Comparing amino acid sequences, which two organisms are the most closely related? How do you know?

    • Question 2: Which organism is most closely related to the turtle? Which is least related to the man?

    • Question 3: Why are some cells blank in the amino acid difference table?

  • Cladogram and Dendrogram Practice:

    • Question 1: Which species developed first: Ferns or Mosses?

    • Question 2: What trait separates lycopods from mosses?

    • Question 3: Would we find a fern fossil in rock 425425 million years old?

    • Question 4: Who is most closely related to the Lancelet?

    • Question 5: Which trait separates the lancelet from the tuna?

    • Question 6: What characteristic does ONLY the leopard have?

  • Spindle Diagram Practice:

    • Question 1: Which group was most diverse in the Jurassic (Jur) period?

    • Question 2: What two groups share the most recent common ancestor?

    • Question 3: What does it mean when the acanthurids and placoderms lines stop?

    • Question 4: What multi-celled organisms evolved first?

    • Question 5: Why does the term "Cambrian Explosion" make sense?

    • Question 6: What abiotic event was necessary for the explosion of life?