Exam 2 Review – Speciation, History of Life, and Prokaryotes
Exam 2 – Chapters 22 – 24
Chapter 22 – How New Species Form (Speciation)
What Defines a Species and How They Stay Separate: We look at different ways to define a 'species'. Think: "How do we know it's a species?"
Morphological Concept: "Morphological, Means Many May Measure by Match!" (If they look alike). Drawbacks: Looks can be deceiving, different species might look similar, or same species might look different (e.g., dog breeds).
Biological Concept: "Biological, Breeding Brings Babies!" (If they can successfully reproduce and have fertile offspring). This is often considered the 'gold standard' but doesn't work for asexual organisms or fossils.
Lineage Concept: "Lineage for Long Lived Legacy!" (If they share a unique evolutionary history, a distinct branch on the tree of life). This is more about their ancestry.
Reproductive Isolation: This is the key. Think: "No 'hanky-panky' allowed!" It's anything that prevents different groups of organisms from mating or producing fertile offspring. This is what keeps species separate and helps new ones form.
Genetic Differences: How small changes in genes (DNA) build up over time to separate groups. Imagine two groups slowly collecting different 'recipes' for life.
Dobzhansky-Muller Model: "DM for Don't Match!" Explains how two different genetic changes, when they finally meet in a hybrid (offspring of two different species), can cause problems, even if each change was fine on its own. It's like having two perfectly good puzzle pieces from different puzzles—they just don't fit together.
How New Species Form (Speciation Types):
Allopatric Speciation: "Allopatric = Apart!" New species form when populations are physically separated, like by a mountain range or an ocean. They evolve in isolation.
Founder Effect: "Founder = Few Far From home!" A small group breaks away from a larger population and starts a new one in a new place. Their gene pool is smaller and different from the parent group.
Ring Species: "Ring = Rounds the Roadblock!" Imagine populations spread around a central barrier (like a desert). Each population along the ring can mate with its neighbors, but by the time the populations meet at the other end of the ring, they've changed so much they can no longer interbreed, even though they can still interbreed with the populations in between them.
Sympatric Speciation: "Sympatric = Same Spot!" New species form while living in the same geographic area. How? Without a physical barrier?
Polyploidy: "Polyploidy = Plenty of Pairs!" This is common in plants. An organism suddenly has extra sets of chromosomes (the organized bundles of DNA).
Autopolyploidy: "Auto = Alone Adding!" The extra chromosome sets come from the same species (e.g., a plant goes from 2n to 4n within itself. It can then only successfully mate with other 4n plants, becoming a new species).
Allopolyploidy: "Allo = Another Adds!" The extra chromosome sets come from the hybridization (mating) of two different species. The hybrid initially might be sterile, but a doubling of its chromosomes can make it fertile, and now it's a new species that can only mate with other allopolyploids.
Ways Species Stay Separate (Isolation Mechanisms): These are the specific 'rules' or barriers that prevent mating or successful reproduction.
Prezygotic (Before Zygote): "PRE-venting the Zygote!" These mechanisms stop mating or fertilization from happening in the first place.
Mnemonic to remember types: "My Tiny Bat Has Green Grapes!" (The last G is for Gametic).
Mechanical: Different body parts just don't fit together (like a lock and key).
Temporal: Different mating times (e.g., one mates in spring, another in fall).
Behavioral: Different courtship rituals or signals (a bird's specific mating dance isn't recognized by another species).
Habitat: Living in different places, even if they're close enough to theoretically meet (e.g., one fish in deep water, another in shallow water).
Gametic: Sperm and egg can't combine, even if mating occurs (chemicals on the egg might only recognize sperm from its own species).
Postzygotic (After Zygote): "POST-Zygote Problems!" These occur after a hybrid offspring is formed, causing issues with its survival or reproduction.
Low Hybrid Vigor: The hybrid offspring are weak or unhealthy and don't thrive.
Adult Viability: The hybrid offspring don't survive to adulthood (they die young).
Hybrid Infertility: The hybrid offspring can't reproduce themselves (e.g., a mule, which is a hybrid of a horse and a donkey, is sterile).
Hybridization and Hybrid Zones: "Hybridization = Half and Half!" This happens when different species interbreed, forming hybrids. Hybrid zones are areas where these hybrids are common. Natural selection can act on these hybrids, sometimes favoring them, sometimes eliminating them, or sometimes leading to reinforcement (where parent species become even more reproductively isolated).
Speciation Rates: The speed at which new species form. Think: "Do they Speed up or Slow down?" Some species form quickly, others very slowly. Scientists investigate how lifestyle might play a role.
Generalists vs. Specialists: Organisms that can live in many different environments and eat many different things (generalists) compared to those that are very particular (specialists). It's thought that specialists might speciate faster because they are so adapted to one specific niche, any slight change or new niche could rapidly lead to divergence.
Chapter 23 – The Story of Life on Earth
Dating Earth's History: "Dating = Determining Due Date!"
Geologic Time Scale: "Earth's Giant Grand Calendar!" The timeline of Earth's history, broken into eons, eras, periods, etc.
Strata: "Strata = Stacks of Stone!" Layers of rock, like pages in Earth's history book, with older layers usually at the bottom.
Radiometric Dating: "Radio for Real Age!" Measuring age using naturally decaying radioactive elements in rocks. It's like a ticking clock in the rocks.
Half-Life: "Half-Life = How Long for Half to Leave!" The specific time it takes for half of a radioactive substance to decay into a stable form. This is the 'rate' of the radiometric clock (e.g., ^{14}C has a half-life of 5,730 years).
Major Eras of Earth's History (Eons): "How Ancient Plants Produced Fantastic Fossils!" (Hadean, Archaen, Proterozoic, Phanerozoic).
Hadean: "Hadean = Hot & Hellish!" The very earliest Earth, before life; molten, hot. The Moon formed then.
Archaeon: "Archaeon = Ancient All Archaea & All Bacteria!" (Emergence of simple prokaryotes).
Proterozoic: "Proterozoic = Proto-Eukaryotes!" (Appearance of more complex cells, like the ancestors of plants, animals, and fungi).
Phanerozoic: "Phanerozoic = Plenty of Fantastic Life!" (The current eon, marked by dramatic diversification of life, including all complex animals and plants).
Geological Changes: "Geological Changes = Ground Constantly Changing!"
Plate Tectonics: "Plates Push and Pull!" The theory that Earth's outer shell is broken into large 'plates' that slowly move, shaping continents, oceans, and influencing evolution (e.g., creating new barriers or connecting landmasses).
Types of Boundaries: "Divide, Collide, Slide!"
Divergent: Plates pull Diverge (apart) -> new crust forms.
Convergent: Plates Converge (collide) -> mountains or volcanoes.
Transform: Plates Transform (slide past each other) -> earthquakes.
Climate Change Effects: "Climate Change = Constant Consequences!"
Milankovitch Cycles: "Milankovitch = Million-year Movements!" Natural, long-term cycles in Earth's orbit and tilt that affect how much sunlight reaches different parts of the Earth, leading to ice ages and warming periods.
Allee Effect: "Allee = Alone, Alas!" A phenomenon where small populations struggle to survive and reproduce effectively because they can't find mates, defend against predators, or forage efficiently. "Too few to thrive!"
Fossil Record Analysis: "Fossils = Finding the Full Story!" Continuing to learn about: layers of rock (strata), the overall life present (biota), animal life (fauna), plant life (flora), and the timeline of major events (extinctions, new life forms) through Earth's long eons and periods.
Chapter 24 – Simple Life Forms: Prokaryotes and Bacteria
Origins and Evolution:
Bacteria and Archaea: "B & A = Before All Else!" These are the earliest and simplest forms of life on Earth.
Lateral Gene Transfer: "Lateral = Leaping Laterally!" Instead of just passing genes from parent to offspring, genes can jump between different, often unrelated, organisms sideways (laterally), kind of like copying and pasting a program from one computer to another, even if they aren't the same model. This makes their phylogenetics (family tree) complicated.
Prokaryote Features: "PRO-karyotes = Primitive ROoms (no nucleus)!" What makes them different from Eukaryotes (complex cells like ours):
They don't have a nucleus (where DNA is stored in complex cells).
They typically lack other internal compartments (organelles) found in eukaryotes.
Have different cell wall structures (e.g., peptidoglycan in bacteria).
Bacterial Classification: Recognize major groups and their features (e.g., Firmicutes, Cyanobacteria).
Ecological Roles: "Ecological Roles = Everywhere Really!"
Biofilms: "Biofilms = Bacterial Band on a Boundary!" Communities of microbes that stick together and to surfaces, often in a slimy protective layer (think plaque on teeth, or pond scum).
Microbiomes: "Microbiome = My Microbes Making My Mouth and Gut!" The collection of all microbes (bacteria, fungi, viruses) living in a particular environment, especially in and on our bodies, playing crucial roles in health.
Infant Microbiome Development: How a baby's first microbes are influenced by its birth method (e.g., passing through the birth canal vs. C-section affects early gut bacteria).
Infectious Prokaryotes and Koch's Postulates: "Infectious = Invaders Irritate!"
Pathogenicity: "Pathogen = Problem-Causing!" The ability of a microbe to cause disease.
Toxigenicity: "Toxin = Toxic Poison!" The ability of a microbe to produce harmful toxins (poisons).
Invasiveness: "Invasive = Into Your Body!" The ability of bacteria to spread through and invade tissues within a host.
Koch's Postulates: "Koch's = Knowing the Killer Cause!" A set of four steps to rigorously prove that a specific microbe causes a specific disease (e.g., find the microbe in sick individuals, isolate it, infect a healthy individual, and re-isolate it).
Viruses: "Viruses = Very Vexing Villains!" Tiny infectious agents that are not considered truly 'alive' because they can only reproduce inside living cells.
Phylogenetic Challenges: It's hard to place viruses on the 'tree of life' because they don't share many genes with cellular life and they evolve rapidly.
Types of Viruses:
Bacteriophages: "Bacterio-Phage = Bac-EATer!" Viruses that specifically infect and kill bacteria.
Retroviruses: "Retro = Reverse (Flow of Information)!" Viruses that have RNA as their genetic material and use an enzyme (reverse transcriptase) to copy their RNA into DNA, which then integrates into the host's DNA (e.g., HIV).
Vaccines: "Vaccines = Victory Versus Viruses!" Preparations that train your immune system to recognize and fight off specific viruses without causing the actual disease.
Vocabulary Review
Species Concepts: Morphological (looks), Biological (breeding), Lineage (ancestry).
Isolation Mechanisms: Prezygotic (before mating/fertilization), Postzygotic (problems after hybrid is formed).
Speciation Concepts: Allopatric (apart), Sympatric (same place), Hybrid (mixing).
Geological Terms: Strata (rock layers), Stratigraphy (study of layers), Half-life (time for half to decay), Plate Tectonics (moving continents).
Bacterial and Viral Terms: Peptidoglycan (bacterial cell wall component), Biofilms (bacterial communities), Koch's Postulates (proving disease cause), Bacteriophage (virus infecting bacteria).
According to the notes, a species can be defined in a few ways, but the most widely accepted definition is the Biological Concept. This concept states that a species is a group of organisms that can successfully reproduce with each other and produce fertile offspring. Other concepts include the Morphological Concept, which defines species based on shared physical appearances, and the Lineage Concept, which focuses on a shared unique evolutionary history.
While species members share common features and can interbreed, genetic diversity within a species is natural and crucial for adaptation. However, the accumulation of genetic differences between different species (as explained by the Dobzhansky-Muller Model) is what eventually prevents successful interbreeding and keeps them separate.