Bio midterm 1

When did earth form

Formed 4.6 billion years ago during the Hadean era

What were the characteristics of the Hadean era

1. Earth formation (very hot and forming internal crust)

2. Moon formation from debris

3. Differentiation of earths layers (iron sinking to core and silicates mantle)

4. Early atmosphere (initially hydrogen and helium)

5. Liquid water during end of era (possible due to high pressure)

6. Possible RNA synthesis and replication and folding active ribozymes

What are the eras of the earth in order

1. Hadean era

2. Archean era

3. Proterozoic

4. Phanerozoic

What is abiogenesis and what are its key steps

The process that gave rise to life on Earth.

Key steps include:

• Formation of organic molecules (e.g., sugars, nucleobases).

• Molecular self-replication (e.g., RNA).

• Self-assembly of protocells.

• Development of LUCA (Last Universal Common Ancestor).

What are the key characteristics of the archean era

1. Frist evidence of rock formation

2. High heat flow (2-3x it is today)

3. Gradual slowing of plate tectonics and crustal recycling (heavy volcanic activity)

4. Limited protection form UV as magnetic field is weak

5. Mostly water world era

6. 3.7 billion years ago → earliest evidence of life on earth

7. 3.5 billlion years ago → earliest identifiable fossils

8. Great oxygenation era

Define prevailing hypothesis of the archean era

Transition from nonliving to living entities not a single event

What characterizes the great oxygenation era

• O2 in water reacts with iron → forms iron oxide (rust).

• Iron oxide builds up into banded iron formations.

• O2 builds up in ocean until it's full.

• 2.7 billion years ago: O2 starts to escape into the atmosphere.

• 2.5 billion years ago: O2 reaches 1-10% of today’s levels → end of the Archean era.

What are stromatolites, and when did they first appear?

microbial layers—they’re the earliest fossils, created by microbes about 3.5 billion years ago, forming layered rocks.

What are the characteristics of the Proterozoic era

1. Changing atmosphere → Oxygen increases, methane drops, ozone forms.

2. First glaciation →Earth freezes for 300 million years

3. Rise of eukaryotic cells → likely through endosymbiosis

4. 1.8 billion years ago → earliest eukaruotic fossil

5. 1.3 billion years ago → multicellular eukaryotes

What signifies the end of the Proterozoic era

1. Increased nutrient availability in oceans and deep water oxygenation

2. O2 increased close to today’s levels → supports more complex and energy demanding life forms

3. Break up of super continent and competition of newly emerging life forms

What is endosymbiosis, and when did eukaryotic cells first appear?

A process where one organism lives inside another, leading to the evolution of eukaryotic cells approximately 2 billion years ago.

What are the characteristics of the Paleozoic era

• Diversity of Life: First vertebrates, plants, and insects.

• Six Major Periods: It consists of the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

• Marine life dominance early on.

• Land colonization by plants and animals.

• Pangaea formed at the end.

What are the key Biological Developments in the Cambrian explosion

• Rapid diversification of life.

• First appearance of hard body parts (e.g., shells, exoskeletons).

• Most major animal phyla (e.g., Arthropoda, Mollusca) originated.

• all appeared over a relatively short geological time

Key Biological Developments in the Silurian period

• First vascular plants on land.

• First terrestrial arthropods (insects and scorpions).

• Evolution of jawed fish.

Key biological developments in Devonian period

• Known as the "Age of Fishes" due to the dominance of fish species.

• First forests and seed-bearing plants.

• First tetrapods (amphibians) and flying insects.

Key biological development in the Carboniferous Period

• Formation of extensive coal swamps due to lush vegetation.

• Amphibians thrived; first reptiles appeared.

• Oxygen levels were very high, enabling large arthropods.

Key biological developments in Permian Period

• Formation of Pangaea.

• Evolution of early conifers and diversification of reptiles.

• Ends with the Permian-Triassic extinction event, the largest mass extinction in Earth's history.

Key characteristic of the Mesozoic era

• Age of reptiles

• Break up of Pangaea - formation of early Atlantic Ocean

• Dominant species are early birds, dinosares, first vertebrates, early mammals…

Key characteristics of Cenozoic era

• age of the mammals

• 3 time periods

1. Paleogene: without dinosaurs → rapid diversification of mammals

2. Neogene: emergence of modern mammal families and bird families

3. Quaternary: age of the ice ages, rise of human and agricultures and civilization

what are the eras of the phaneorozoic eon

1. Paleozoic

2. Mesozoic

3. Cenozoic

What is the main focus of evolutionary theory?

Focuses on how life changed after its origin, not the origin of life itself.

Who was Charles Darwin, and why is he important?

A naturalist who developed the theory of descent with modification through natural selection.

Is evolution a theory about the origin of life?

No, it explains how life changes over time after it originated.

Does evolution mean organisms are always getting better?

No, it is about reproductive fitness in a given environment, not progress toward perfection.

Is evolutionary change purely random?

Not entirely. happens randomly, but only beneficial ones that help survival and reproduction stick around.

Does natural selection involve organisms actively trying to adapt?

No, it occurs through selection acting on genetic variation, not an organism’s effort to change.

Does natural selection give organisms what they need?

No, it has no intent; it selects traits already present in the population that improve survival.

What was Lamarck’s theory of evolution?

proposed "inheritance of acquired characteristics," suggesting that organisms develop traits in response to use or disuse.

Why was Lamarck’s theory rejected?

It failed to explain vestigial structures and lacked genetic evidence supporting acquired trait inheritance.

What are vestigial structures?

Body parts that have lost their original function through evolution (e.g., human appendix, whale pelvis)

How did Malthus influence Darwin?

He noted that populations grow faster than food supplies, leading to competition and survival of the fittest.

How did artificial selection contribute to Darwin’s theory?

He saw that humans could breed for desirable traits in plants and animals, suggesting nature could do the same over time.

What are the four key components of natural selection?

1. Variation in traits within a population.

2. Some traits offer a survival or reproductive advantage.

3. Traits must be heritable.

4. Over time, advantageous traits become more common.

How does natural selection lead to speciation?

When populations with different traits become reproductively isolated, they may evolve into new species.

Why do species go extinct?

If they cannot adapt quickly enough to changing environments, they may die out.

What is homology?

Similar structures in different species due to common ancestry (e.g., human, bat, and seal forelimbs).

What is the fossil record, and why is it important?

It provides physical evidence of transitional species and evolutionary change over time.

What are transitional fossils?

Show intermediate traits between ancient and modern species, helping us see how evolution happens over time.

How does biogeography support evolution?

The geographic distribution of species reflects evolutionary history and continental drift (e.g., Pangaea).

What are some direct observations of evolution in action?

• Pesticide resistance in insects.

• Antibiotic resistance in bacteria.

• Darwin’s finches adapting to different food sources.

How has human activity accelerated natural selection?

Pollution, habitat destruction, climate change, and selective breeding have altered evolutionary pressures.

What is the “pesticide treadmill”?

The cycle in which pests evolve resistance to pesticides, requiring stronger chemicals, which pests again resist.

What are GMOs, and how do they relate to evolution?

Genetically modified organisms have altered traits that affect their fitness and evolutionary potential.

what was the theory of “Use and disuse”

develped by lamark

body parts used frequently gets stronger and more developed as generations enfold, those not used detoriate over time

is evolution just a theory

yes

what is a theory in science

explanation of some aspect of the natural world well-substantiated by multiple lines of independent evidence

what is an analogous structure

features of specied that are similar in function but not in structure - do not derive from same ancestor

What are the four main lines of evidence for evolution?

1. Direct Observation

2. Homology

3. Fossil Record

4. Biogeography

what is Direct Observation

Seeing evolution happen in real time (e.g., antibiotic resistance in bacteria).

what is Fossil Record

Preserved remains of past organisms showing how organisms changed over time.

what is Biogeography

The distribution of species across the world, showing how geography influences evolution.

Does evolution work on the individual level?

no,  It operates on the population level, where genetic variation and changes in allele frequencies occur over generations.

What is the importance of genetic variation in evolution?

 without it, evolution is impossible. It provides the raw material for natural selection and other evolutionary mechanisms to act upon.

What are the three main sources of new genetic variations in a population

1. Mutation in germ lines

2. Chromosomal changes 

3. Sexual reproduction 

How does mutation contribute to genetic variation?

Mutations in germ lines create new alleles, which are changes in heritable DNA. These mutations can be neutral, deleterious, lethal, or advantageous.

What is the role of meiosis in generating genetic variation?

1. Recombination/crossing over (Prophase I), which creates new combinations of alleles on chromatids.

2. Independent assortment (Metaphase I & Anaphase I), where homologous chromosomes align randomly, leading to diverse gametes.

What is the Hardy-Weinberg Equilibrium, and what does it assume?

The null model assumes:

• No mutations

• No immigration

• A large population

• Equal fitness for all genotypes

• Random mating

If these conditions hold, allele frequencies stay the same, meaning no evolution.

What happens if the assumptions of the Hardy-Weinberg Equilibrium are violated?

allele frequencies will change, and evolution (microevolution) will occur.

What are the five mechanisms that can alter allele frequencies in a population?

1. Mutations (introduce new alleles).

2. Gene flow (immigration/emigration).

3. Genetic drift (random changes in small populations).

4. Natural selection (differential survival and reproduction).

5. Nonrandom mating (e.g., inbreeding).

What is genetic drift, and how does it affect small populations?

the random change in allele frequencies due to chance events, especially in small populations. It can lead to the loss of genetic diversity and the fixation of alleles.

What are the two main effects of genetic drift?

1. Bottleneck Effect: A sharp reduction in population size due to events like natural disasters, leading to reduced genetic diversity.

2. Founder Effect: When a small group establishes a new population, leading to reduced genetic variation compared to the original population.

What is natural selection, and how does it lead to adaptive evolution?

the process where traits that enhance survival or reproduction become more common in a population It causes adaptive evolution by favoring alleles that improve fitness.

What are the three types of natural selection?

1. Directional : Favors one extreme phenotype.

2. Stabilizing : Favors intermediate phenotypes.

3. Disruptive : Favors both extreme phenotypes over the intermediate.

What is heterozygosity, and how is it measured?

Genetic diversity at one locus, calculated as H = 2pq, where p and q are allele frequencies.

How is average heterozygosity (Have) calculated across multiple loci?

 Average heterozygosity (Have) is calculated by averaging the heterozygosity values across many loci in a population. It provides a measure of overall genetic diversity.

 What is the significance of the Hardy-Weinberg equation?

The Hardy-Weinberg equation p2+2pq+q2=1 predicts the genotype frequencies in a non-evolving population and checks if it's in genetic equilibrium.

What is the difference between observed heterozygosity (Ho) and expected heterozygosity (He)?

• Observed heterozygosity (Ho) → Actual heterozygotes in a population (what you see).

• Expected heterozygosity (He) → What you’d expect based on Hardy-Weinberg (ideal conditions).

What is the inbreeding coefficient, and how is it calculated?

measures how much inbreeding reduces genetic diversity (heterozygosity) in a population.

F=1−Ho/He​
where Ho is observed heterozygosity and He is expected heterozygosity.

• If F = 0, there’s no inbreeding (Ho = He).

• If F = 1, there’s complete inbreeding (no heterozygosity).

What is balancing selection, and how does it maintain genetic variation?

it maintains multiple alleles in a population through mechanisms like:

1. Heterozygous advantage (e.g., sickle cell anemia).

2. Frequency-dependent selection (fitness depends on allele frequency).

3. Habitat selection (different alleles favored in different environments).

 What is the difference between gene flow and genetic drift?

• Gene flow: The movement of alleles between populations through migration, which can increase genetic diversity.

• Genetic drift: Random changes in allele frequencies, especially in small populations, which can reduce genetic diversity.

What is the role of mutations in evolution?

mutations create new genetic variations (new alleles) that evolution can act upon

What is the difference between microevolution and macroevolution?

• Microevolution: Small-scale changes in allele frequencies within a population over a short time.

• Macroevolution: Large-scale changes, such as the formation of new species, over long periods.

What is the role of sexual reproduction in generating genetic variation?

1. Recombination during meiosis.

2. Independent assortment of chromosomes.

3. Fertilization, which combines alleles from two parents.

What is the difference between a population and a species?

• Population: A group of individuals of the same species living in the same area and interbreeding.

• Species: A group of organisms capable of interbreeding and producing fertile offspring.

 What is the significance of genetic diversity in endangered species?

Low genetic diversity = more risk of disease and extinction. Conservation protects diversity to save species.

what is evolution a blend of

chance: creating new genetic variations (through mutation)

sorting: natural selection favoring some alleles over others

what does natural selection do

1. increases alleles frequency that enhance reproduction or survival

2. increase these frquencies in one of: directional selection, stabilizing selection, or disruptive selection

3. reduces unfavorable traits

what is dipoloity

state of having 2 complete sets of chromosomes in a cell or organism

what is balancing selection

maintains genetic diversity in a population (reduces likelihood of allele fixation)

define heterozygous advantage

when a heterozygote has a higher fitness than a homozygote

define frequency dependent fixation

fitness is dependent upon the frequency of phenotype or genotype in a population.

What evidence suggests that life on Earth existed 3.5 billion years ago?

Fossilized stromatolites.

What is the significance of adaptive radiations?

They involve the rapid diversification of species to fill ecological niches.

What event is associated with the Great Oxygenation Event?

The rise of atmospheric oxygen due to photosynthesis.

Which mass extinction is considered the most severe in Earth’s history?

The Permian extinction.

What adaptation helped plants colonize land approximately 500 million years ago?

The formation of vascular tissue and protective coatings.

What defines adaptive radiation?

 The evolution of a species into several forms to fill different niches.

Why is the fossil record considered incomplete?

It is biased toward organisms with hard parts and favorable preservation conditions.

What major evolutionary event occurred during the Proterozoic eon?

The rise of eukaryotic cells and the first multicellular organisms.

Serial endosymbiosis

suggests eukaryotes evolved when larger cells engulfed smaller prokaryotes, which became mitochondria and chloroplasts.

Plate tectonics

The theory is that the continents sit on large plates that float on Earth's hot mantle. Mantle movements make the continents slowly drift over time.

Paedomorphosis

The retention in an adult organism of the juvenile features of its evolutionary ancestors.

Convergent evolution

when different species evolve similar traits independently.

Sexual dimorphism

Differences between the secondary sex characteristics of males and females.

What is the biological species concept?

The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring in nature. Reproductive isolation (preventing gene flow) is key to this concept.

What are the prezygotic barriers to reproduction?

 prevent fertilization and include:

1. Habitat isolation: Species live in different habitats.

2. Temporal isolation: Species breed at different times.

3. Behavioral isolation: Species have different mating rituals.

4. Mechanical isolation: Physical differences prevent mating.

5. Gametic isolation: Sperm and egg are incompatible

What are the postzygotic barriers to reproduction?

reduce the viability and fertility of hybrids:

1. Reduced hybrid viability: Hybrids don’t survive well.

2. Reduced hybrid fertility: Hybrids can’t reproduce (e.g., mules).

3. Hybrid breakdown: First-generation hybrids are viable, but second-generation hybrids are not.

What is reproductive isolation?

the accumulation of genetic differences that prevent two populations from interbreeding. It can be caused by prezygotic or postzygotic barriers.

What is allopatric speciation?

When two populations are separated by geography, they stop sharing genes. Over time, they become different species.

What is sympatric speciation?

New species form in the same area without physical separation due to ecological, behavioral, or genetic factors.