Organismal Bio TXST Final

How does ploidy change with Meiosis?

Ploidy changes from diploid (2n) to haploid (n) during meiosis, producing four haploid gametes.

How does Meiosis result in genetically distinct daughter cells, thus resulting in the potential for diverse offspring.

How does Meiosis result in genetically distinct daughter cells, thus resulting in the potential for diverse offspring.

 What are the genotype ratios at each step? What are the phenotype ratios at each step?

monohybrid cross (one gene, heterozygous parents, Aa × Aa):

• Phenotype Ratio: 3:1 (3 dominant : 1 recessive).

dihybrid cross (two genes, heterozygous parents, AaBb × AaBb):

• Phenotype Ratio: 9:3:3:1 (9 dominant for both traits, 3 dominant for one trait and recessive for the other, 3 vice versa, 1 recessive for both traits).

• Monohybrid Cross (Aa × Aa):

  • Genotype Ratio:
    1:2:1
    (1 homozygous dominant: 2 heterozygous: 1 homozygous recessive).

  • Dihybrid Cross (AaBb × AaBb):

    • Genotype Ratio:
      1:2:1:2:4:2:1:2:1
      (Reflecting combinations of homozygous and heterozygous genotypes for two genes).

Understand how dihybrid crosses explain how meiosis works.... unless the, of course, the traits chosen are linked.

dihybrid cross demonstrates meiosis by showing how segregation separates alleles (A/a, B/b) into gametes and how independent assortment mixes them. This creates genetic diversity, leading to a 9:3:3:1 phenotype ratio in offspring.

Be able to define evolution using our technical definition.

Evolution is the change in the genetic composition of a population over successive generations, driven by mechanisms such as natural selection, genetic drift, mutation, and gene flow. These changes can lead to the development of new traits or species over time.

Know the major influences for Darwin.

Darwin was influenced by:

1. Lamarck: Species change over time.

2. Lyell: Earth changes gradually.

3. Malthus: Populations compete for resources.

4. Artificial Selection: Breeding shows traits can change over generations.

These ideas helped him develop natural selection.

What are fossils? Where are they found (type of rock)? How are they dated (relatively and absolute)? Why do we consider the fossil record incomplete?

Fossils are remains or traces of ancient organisms, found in sedimentary rocks. They are dated by relative dating (position in rock layers) and absolute dating (radiometric methods). The fossil record is incomplete due to factors like poor preservation, erosion, and rare fossilization.

What is homology? (How does this relate to synapomorphy & phylogenetic trees? – Ch 25) What is differential fitness? How does understanding homology show the pattern of evolution, while differential fitness shows one of the processes?

Homology is similarity due to shared ancestry, shown in synapomorphies (shared traits) used to build phylogenetic trees.

Differential fitness refers to how certain traits improve survival and reproduction, driving natural selection.

Homology shows the pattern of evolution (common ancestry), while differential fitness explains the process (natural selection).

What are Darwin’s four postulates? Where does heritable variation originate? What are the relationships between natural selection, fitness and adaptation? (How does the nature of variation needed for selection explain why some populations will respond to climate change and other threats to biodiversity with adaptation, while others will go extinct? –chapter 53-54)

Darwin’s Four Postulates:

1. Variation exists in traits.

2. Traits are heritable.

3. Some individuals survive and reproduce better.

4. Beneficial traits become more common.

Heritable Variation Origins:

Variation comes from mutations, genetic recombination, and gene flow.

Natural Selection, Fitness, and Adaptation:

• Natural selection increases fitness, leading to adaptation over time.

Climate Change Response:

Populations with genetic variation can adapt to changes, while those without may face extinction.

Understand the four modes of selection. (How does directional selection relate to character displacement often occurring with competition? Chapter 52)

Four Modes of Selection:

1. Directional: Favors one extreme trait (e.g., larger beaks).

2. Stabilizing: Favors the average trait (e.g., average birth weight).

3. Disruptive: Favors both extremes (e.g., small and large beaks).

4. Balancing: Maintains genetic diversity (e.g., sickle cell in humans).

Directional Selection & Character Displacement:

Directional selection .can cause character displacement, where species evolve different traits to reduce competition, like birds with different beak sizes.

How does sexual selection differ from natural selection? Why might this be in tension with natural selection?

Sexual selection favors traits that increase mating success, while natural selection favors traits that enhance survival. They can be in tension because traits that are good for mating (e.g., bright colors) may reduce survival.

What is genetic drift? How does drift relate to fitness? How does population size determine how strongly drift can cause populations to evolve? How does drift affect genetic variability?

Genetic drift is the random change in allele frequencies, especially in small populations. It doesn't favor fitness traits but can randomly increase or decrease alleles. Smaller populations are more affected by drift, leading to less genetic variability over time

What is gene flow? How does gene flow relate to fitness? How does gene flow affect genetic variability?

Gene flow is the movement of alleles between populations. It can increase fitness by adding beneficial alleles and boosts genetic variability by introducing new genes.

Know the species concepts presented in class. What are the advantages/disadvantages of each? Why can there be no single definition of a species?

Species Concepts:

1. BSC: Species are interbreeding, reproductively isolated groups.

   • Pros: Focuses on isolation.

   • Cons: Doesn’t apply to asexual organisms.

2. Morphological: Species are defined by physical traits.

   • Pros: Works for fossils and asexuals.

   • Cons: Doesn’t show genetic isolation.

3. Phylogenetic: Species are the smallest groups sharing a common ancestor.

   • Pros: Based on evolutionary history.

   • Cons: Requires detailed data.

4. Ecological: Species are defined by their niche.

   • Pros: Works for asexuals.

   • Cons: Niche overlap complicates definitions.

Why No Single Definition?

Species vary across contexts, and boundaries can be fluid due to hybridization or asexual reproduction.

How does allopatric speciation differ from sympatric speciation? What are reproductive barriers?

Allopatric vs. Sympatric Speciation:

• Allopatric: Speciation due to geographic isolation.

• Sympatric: Speciation without geographic isolation, often due to genetic or ecological factors.

Reproductive Barriers:

• Prezygotic: Barriers before fertilization (e.g., behavior, timing).

• Postzygotic: Barriers after fertilization (e.g., hybrid sterility).

What are phylogenies? how they are made... and how they are tested? 

Phylogenies are trees that show evolutionary relationships. They are made by comparing shared traits (morphological or genetic) and tested by comparing with fossil/genetic data and using statistical methods to find the most likely tree.

Why is no single phylogeny considered absolutely correct? How might convergent evolution or losses of traits result in an incorrect phylogeny?

No phylogeny is absolutely correct because of factors like convergent evolution (unrelated species developing similar traits) and loss of traits (missing features that complicate ancestry). These can lead to misleading conclusions about evolutionary relationships.

What are mass extinctions? (Why do we think we’re in the sixth mass extinction event? Ch 53-54) How do mass extinction events relate to adaptive radiation? What is the pattern of these in the fossil record?

Mass extinctions are rapid losses of species. The sixth mass extinction is happening due to human impact. After mass extinctions, adaptive radiation occurs, with surviving species rapidly diversifying. Fossils show this pattern of rapid new species.

(How are bacteria particularly important for biogeochemical cycles? Ch53)

Bacteria are crucial for biogeochemical cycles because they decompose organic matter, recycle nutrients (like nitrogen and carbon), and convert elements into forms plants and animals can use. For example, nitrogen-fixing bacteria convert nitrogen gas into usable forms for plants.

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How do bacteria of completely different species... that haven’t shared common ancestors in billions of years... able to share genes?

Bacteria share genes through horizontal gene transfer (HGT), which includes transformation, transduction, and conjugation. This allows genetic exchange between species, even without common ancestry.

What are Archaea? How do they relate to bacteria and to us, as Eukaryotes?

Archaea are single-celled organisms similar to bacteria but genetically closer to eukaryotes (like humans). They share some features with eukaryotes, such as ribosome structure, and are more closely related to eukaryotes than to bacteria. Archaea thrive in extreme environments but also live in common habitats.

Understand endosymbiotic theory.... including the two major events. How does the first event to occur explain why all eukaryotes (including plants) perform cellular respiration? How does the second event explain why plants, green algae and red algae perform photosynthesis?

The endosymbiotic theory states mitochondria and chloroplasts were once free-living bacteria engulfed by eukaryotes.

1. Mitochondrial endosymbiosis explains why all eukaryotes perform cellular respiration.

2. Chloroplast endosymbiosis explains why plants, green algae, and red algae perform photosynthesis.

Know the plant phylogeny and the synapomorphies unifying each lineage.

Plant Phylogeny and Synapomorphies:

1. Non-Vascular Plants (Bryophytes): No vascular tissue, depend on water for reproduction (e.g., mosses).

2. Vascular Plants: Have vascular tissue (xylem and phloem). Includes:

   • Seedless Vascular Plants: Vascular tissue, reproduce via spores (e.g., ferns).

   • Seed Plants: Have seeds for reproduction. Divided into:

     • Gymnosperms: Naked seeds (e.g., conifers).

     • Angiosperms: Flowers and fruits (e.g., flowering plants).

How does the seed compare/contrast to the amniotic egg – Ch 32?

Seed vs. Amniotic Egg:

• Similarities: Both protect the embryo and provide nutrients.

• Differences:

  • Seed: Found in plants, can remain dormant and germinate when conditions are right.

  • Amniotic Egg: Found in reptiles, birds, and some mammals, with membranes that protect the embryo on land.

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What role do plants play in food webs & energy/matter flux in ecosystems, and biogeochemical cycles

Plants are primary producers in food webs, converting sunlight into energy through photosynthesis. They contribute to energy flow and matter cycling by supporting herbivores, decomposers, and recycling nutrients in biogeochemical cycles like carbon and nitrogen.

What types of community interactions are plants involved in

Plants are involved in various community interactions, including:

1. Competition: Competing for light, water, and nutrients.

2. Mutualism: Benefiting from relationships, like with pollinators or mycorrhizal fungi.

3. Herbivory: Being eaten by herbivores.

4. Predation: Some plants may trap and digest animals (e.g., carnivorous plants).

5. Allelopathy: Releasing chemicals that inhibit the growth of nearby plants.

6. Commensalism: Providing support for epiphytic plants without harming them (e.g., trees hosting orchids).

What ecosystem service roles do plants play?

Plants provide several essential ecosystem services, including:

1. Oxygen Production: Through photosynthesis, plants release oxygen.

2. Carbon Sequestration: Plants absorb carbon dioxide, helping to mitigate climate change.

3. Soil Stabilization: Plant roots prevent soil erosion.

4. Water Regulation: Plants help in water filtration and maintain the water cycle.

5. Habitat: Provide shelter and food for animals.

6. Pollination: Support pollinators that are vital for crop production.

7. Nutrient Cycling: Help recycle nutrients through decomposition and interactions with soil organisms.

How do fungi get matter and energy? How is this like us? Unlike us? What major role do fungi play in ecosystems (and biogeochemical cycles – Ch 53)? (What other types of interactions do fungi have with other organisms? Ch 52)

How Fungi Get Matter and Energy:

• Fungi are heterotrophs that absorb nutrients by breaking down organic material externally.

• Like us: Both are heterotrophs.

• Unlike us: Fungi digest food externally, while we digest it internally.

Role in Ecosystems:

• Fungi are decomposers, recycling nutrients and supporting biogeochemical cycles.

Interactions with Organisms:

1. Mutualism: E.g., mycorrhizae with plants.

2. Parasitism: Fungi can be pathogens.

3. Commensalism: E.g., lichen living on trees.

Why is fungal sex weird from our animal perspective?

Fungal sex is "weird" because:

1. Mating Types: Fungi have multiple mating types instead of male and female.

2. Heterokaryosis: Fungi can have two different nuclei in one cell before fusion, unlike animals.

3. No Distinct Sexes: Fungi don't have clear sexes; reproduction depends on genetic compatibility.

Know the animal phylogeny and the synapomorphies.

Animal Phylogeny and Synapomorphies:

1. Porifera (Sponges): No true tissues or organs.

2. Eumetazoa: True tissues and symmetry.

   • Cnidaria: Radial symmetry, cnidocytes for prey capture.

3. Bilateria: Bilateral symmetry, three germ layers.

   • Protostomes: Mouth forms first during development.

   • Deuterostomes: Anus forms first.

4. Chordata: Notochord, dorsal nerve cord, pharyngeal slits.

   • Vertebrates: Backbone and cranium.

What are animals? How do these differ from other organisms? How are they the same/different with respect to obtaining matter and energy and reproduction? 

What Are Animals?

Animals are multicellular, eukaryotic, heterotrophic organisms with specialized tissues.

Differences:

• Plants: Autotrophic, with cell walls.

• Fungi: Heterotrophic, absorb nutrients externally.

Matter and Energy:

• Same: All obtain energy from organic matter.

• Different: Animals ingest food; plants synthesize it; fungi absorb it.

Reproduction:

• Same: Most animals reproduce sexually.

• Different: Animals have specialized reproductive structures.

How do chordates relate to vertebrates? What are amniotes? (How does the amniotic egg compare/contrast with the seed – Ch 28?)

Chordates are animals with a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail at some stage. Vertebrates are a subgroup of chordates that have a backbone.

Amniotes are vertebrates that lay eggs with specialized membranes (like the amniotic egg) or give birth to young that develop in such membranes. This includes reptiles, birds, and mammals.

The amniotic egg has protective membranes (amniotic sac, yolk, etc.) that support development on land.

Comparing it to the seed: Both protect the embryo, but the amniotic egg is an animal reproductive structure, while the seed is a plant structure for growth and dispersal.

How do modern humans classify as homonins, homonids, anthropoids and primates? Why is human evolution a radiation... not a linear progression?.

Humans are classified as:

• Primates: We belong to the order of primates, which includes all monkeys, apes, and humans.

• Anthropoids: We are part of this suborder, which includes monkeys, apes, and humans, characterized by larger brains and complex behavior.

• Hominids: We belong to this family, which includes great apes and humans, sharing traits like large brains and upright posture.

• Hominins: This group includes humans and our closest extinct relatives, defined by traits like bipedalism and larger brains.

Human evolution is a radiation because it involved branching into different species, rather than a linear progression, with various human ancestors evolving and coexisting at different times.

What is the currently accepted hypotheses regarding how do modern humans relate to each other?

The two main hypotheses for how modern humans relate to each other are:

1. Out of Africa Hypothesis: Modern humans evolved in Africa and then migrated, interbreeding with archaic humans like Neanderthals and Denisovans.

2. Multiregional Hypothesis: Modern humans evolved in different regions from local populations of earlier humans, with gene flow between regions.

The Out of Africa hypothesis is most widely supported, with evidence of interbreeding and Africa as the primary origin.

Know the difference between range and niche. How are niches multi-dimensional? What sorts of things (in general) define niches for various organisms?

• Range: The geographic area where a species can be found.

• Niche: The role of a species in its environment, including its habitat, food sources, and interactions.

Niches are multi-dimensional because they involve space, time, resources, and interactions with other species.

Niches are defined by:

• Physical conditions (e.g., temperature, light),

• Food sources,

• Behavior (e.g., activity patterns),

• Species interactions (e.g., competition, predation).

What’s the difference between weather and climate? What things determine what climate is like in any one location on earth?

• Weather is short-term atmospheric conditions (hours or days), while climate is the long-term average of weather patterns (over 30 years).

Factors determining climate:

1. Latitude: Affects temperature based on sunlight.

2. Altitude: Higher elevations are cooler.

3. Proximity to Water: Moderates temperatures.

4. Ocean Currents: Influence temperature and precipitation.

5. Wind Patterns: Distribute heat and moisture.

6. Topography: Mountains affect precipitation.

7. Human Activity: Alters local and global climates.

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How does climate relate to biomes?

Climate determines the characteristics of biomes based on temperature and precipitation. For example:

• Tropical rainforests are warm and wet.

• Deserts are hot and dry.

• Tundras are cold and dry.

The climate shapes the distribution and adaptation of species in each biome.

How do ultimate causes of behavior differ from proximate causes of behavior?

Proximate causes explain how a behavior happens (e.g., physiological or environmental triggers).
Ultimate causes explain why a behavior exists, often in terms of evolutionary benefits (e.g., survival or reproduction).

How does reciprocity differ from altruism? How does Hamilton’s rule work with respect to predicting altruism?

Reciprocity involves helping with the expectation of future help, while altruism is helping without expecting anything in return.

Hamilton's Rule:

It predicts altruism when helping relatives (kin) if the benefit to the relative (r * B) outweighs the cost to the helper (C), where r is genetic relatedness.

How do populations get larger and smaller?

Populations get larger through births and immigration, and smaller through deaths and emigration.

What’s the difference between exponential and logistic population growth?

Exponential growth is rapid and unlimited, forming a J-shaped curve.
Logistic growth slows as the population reaches its carrying capacity, forming an S-shaped curve.

How does K relate to density dependence? (How does human activities affect K for a variety of organisms, including our own? – Ch 54)

K is the carrying capacity, limited by factors like food and disease. Humans affect K by altering resources, habitats, and the environment, impacting population size for many species, including ourselves.

What are the four types of interactions between species? How is fitness affected in each? (Why do these interactions (except the commensal “0”), by necessity relate to how populations evolve – Ch 22)

The four species interactions are:

1. Competition: Both species are harmed.

   • Fitness: Both species' fitness decreases.

2. Predation: Predator benefits, prey is harmed.

   • Fitness: Predator's fitness increases, prey's decreases.

3. Mutualism: Both species benefit.

   • Fitness: Both species' fitness increases.

4. Commensalism: One benefits, the other is unaffected.

   • Fitness: The benefiting species' fitness increases.

These interactions affect fitness and drive evolution by influencing survival and reproduction.

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What is community structure? And how is it measured/compared between communities?

Measuring and Comparing Communities:

Community structure is measured by:

• Species diversity indices (e.g., Shannon index) that combine richness and evenness.

• Species composition: The types of species present.

• Abundance: The number of individuals per species.

Communities are compared by examining these factors to identify differences in species diversity, dominance, and interactions.

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How does matter and energy flow through ecosystems? What is the general pattern for exchange between trophic levels in terrestrial ecosystems?

In ecosystems, energy flows one-way: from the sun to producers, then to consumers, with energy lost as heat at each trophic level (about 10% transfer). Matter cycles, with nutrients recycled by decomposers.

Trophic Levels in Terrestrial Ecosystems:

1. Producers (plants) capture solar energy.

2. Primary consumers (herbivores) eat plants.

3. Secondary consumers (carnivores) eat herbivores.

4. Tertiary consumers eat other carnivores.

5. Decomposers recycle nutrients.

Energy decreases at higher levels, while matter is recycled.

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What are biogeochemical cycles? How have humans altered biogeochemical cycles?

Biogeochemical cycles are processes through which elements like carbon, nitrogen, and phosphorus move through ecosystems.

Human Impact:

• Carbon cycle: Increased CO2 from burning fossil fuels and deforestation, contributing to climate change.

• Nitrogen cycle: Excess nitrogen from fertilizers leads to water pollution.

• Phosphorus cycle: Overuse of phosphorus fertilizers causes nutrient pollution.

These disruptions cause issues like climate change, pollution, and biodiversity loss.

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What is climate change? How does recent climate change (i.e. global warming) relate to altered biogeochemical cycles?

Climate change refers to long-term shifts in Earth's weather patterns, with global warming being the recent rise in temperatures due to human activities like burning fossil fuels.

Connection to Biogeochemical Cycles:

• Carbon cycle: More CO2 from fossil fuels intensifies global warming.

• Nitrogen and phosphorus cycles: Climate changes affect nutrient movement, worsening ecosystem disruptions.

These changes in cycles contribute to and amplify global warming and environmental issues.

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How are populations of organisms responding to climate change? (how does this relate to genetic variability, adaptation and selection? Ch 22, 23, 54)

Populations respond to climate change by shifting distribution, changing phenology, and altering behavior. These responses are driven by genetic variability, where natural selection favors individuals better suited to new conditions. Over time, populations may adapt to climate changes, with beneficial traits becoming more common.

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What are the three components of diversity? How does each increase? Decrease? From the perspectives of populations (or communities/ecosystems), why is higher diversity better than lower diversity?

The three components of diversity are:

1. Species Richness: Number of species.

   • Increases with immigration and resources, decreases with habitat loss.

2. Species Evenness: Distribution of individuals among species.

   • Increases with balanced resource sharing, decreases with dominance of one species.

3. Genetic Diversity: Genetic variation within a species.

   • Increases with gene flow, decreases with inbreeding.

Why Higher Diversity is Better:

Higher diversity improves ecosystem stability, resource efficiency, and adaptability, making ecosystems more resilient to change and stress

What are ecosystem services? How do these relate to food-webs, biogeochemical cycles, and resilience/resistance to disturbance?

Ecosystem services are benefits like clean air, water, and food.

• Food webs: Support pollination and pest control.

• Biogeochemical cycles: Help maintain soil and water quality.

• Resilience: Healthy ecosystems recover from disturbances, supporting stability.

These services rely on food webs, nutrient cycles, and ecosystem resilience.