describe the evolution of eurkaryotes from the first primitive prokaryotes
the first cells were there 3.7 BYA in stromatolites
1. these cells were anerobic heterotrophic prokaryotes that used fermentation (anerobic process) to remove small amounts of energy from glucose and other sugars in the absence of oxygen
there is a shortage of nutrients for the primitive prokaryotes → means an autotroph needs to develop
2. early autotrophs broke down H2S using chemical energy and sunlight
then there is a shortage of H2S and organisms capable of breaking down H2O formed because there was a lot of water
3. autotrophs 2.0: can break down water
this makes the environment aerobic
aerobic processes evolved:
cellular respiration
aerobic metabolism
this changing environment meant heterotrophs needed to find food differently
4. increase in protiens needed for heterotrophs in order to find food, eat and process food
more protiens means more DNA needed to make the new proteins
5. evolution of the nucleus (protects DNA)
6. eukaryotes evolved 2bya → true nucleus = eukaryote
how did other membrane bound organelles evolve
these evolved as the membrane took different shapes and pinched in forming internal compartments where chemical processes could take place, becoming their own distinct membrane bound organelles
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describe the evolution of eurkaryotes from the first primitive prokaryotes
the first cells were there 3.7 BYA in stromatolites
1. these cells were anerobic heterotrophic prokaryotes that used fermentation (anerobic process) to remove small amounts of energy from glucose and other sugars in the absence of oxygen
there is a shortage of nutrients for the primitive prokaryotes → means an autotroph needs to develop
2. early autotrophs broke down H2S using chemical energy and sunlight
then there is a shortage of H2S and organisms capable of breaking down H2O formed because there was a lot of water
3. autotrophs 2.0: can break down water
this makes the environment aerobic
aerobic processes evolved:
cellular respiration
aerobic metabolism
this changing environment meant heterotrophs needed to find food differently
4. increase in protiens needed for heterotrophs in order to find food, eat and process food
more protiens means more DNA needed to make the new proteins
5. evolution of the nucleus (protects DNA)
6. eukaryotes evolved 2bya → true nucleus = eukaryote
how did other membrane bound organelles evolve
these evolved as the membrane took different shapes and pinched in forming internal compartments where chemical processes could take place, becoming their own distinct membrane bound organelles
explain the theory of endosymbiosis
primary and secondary endosymbiosis
when a larger cell takes in a smaller cell by a process called endocytosis, so the smaller cell is inside a vesicle in the cytoplasm of the larger cell
gives the smaller cell protection
gives the larger cell energy made by smaller cell
endosymbiosis is thought to have occured 2x:
primary endosymbiosis: the anerobic heterotroph eats aerobic prokaryote → mitochondria
secondary endosymbiosis: aerobic heterotrophs eats autotrophic photosynthetic prokaryote →chloroplasts
explain the support for the theory of endosymbiosis in the evolution of mitochondria and chloroplasts (4)
grow and divide indepently of the cell in which they exist
have no nucleus, just a naked loop of DNA
make some of their own protiens using 70S ribosomes like prokaryotes
have double membranes → from being engulfed in a vesicle
when did organisms evolve to become multicellular
750 mya
what was the cambrian explosion
what factors allowed it to happen?
rapid period of speciation and diversification that took place about 541 mya
increase in oxygen, more nutrients available and more predators which drove prey to evolve faster and imrpove their defenses
what are the 2 speeds in which evolution can take place?
gradualism: small genetic changes that occur over time
punctuated equilibrium: sudden evironmental changes that produce rapid evolution → rapid speciation
Does evolution occur due to small changes over time, large environmental shifts, or both?
✅ Both.
Gradualism: Evolution occurs through the accumulation of small genetic changes over long periods of time.
Punctuated Equilibrium: Sudden environmental changes (like climate shifts, disasters, or new habitats) can cause rapid speciation events.
What makes organisms within a species different from other species?
Organisms within a species:
Can interbreed and produce fertile offspring.
Share similar genetic and physical characteristics.
What do we call it when a new species is formed?
✅ Speciation
Speciation is the process by which new species evolve from a common ancestor.
Can happen due to geographic isolation (allopatric speciation), behavioral changes, or genetic divergence.
microevolution vs macroevolution:
definitions
time scale
processes involved
scope
Feature | Microevolution | Macroevolution |
---|---|---|
Definition | the changes in allele frequency within a population | Large-scale evolutionary changes that result in the formation of new species or higher taxonomic groups |
Time scale | Short-term (within a few generations) | Long-term (thousands to millions of years) |
Examples | - Antibiotic resistance in bacteria- Color variation in moths- Beak size changes in finches | - Evolution of birds from dinosaurs- Speciation of humans and chimpanzees from a common ancestor |
Processes involved | - Mutation- Natural selection- Gene flow- Genetic drift | - All of the above, plus- Speciation- Mass extinction- Adaptive radiation |
Scope | Affects allele frequencies within a single population | Affects entire lineages and may span across multiple species |
microevolution = small genetic changes within a species
macroevolution = accumulation of those changes over time that leads to new species or groups
what are the 5 aspects of evolution?
adaptations
movement (gene flow)
mutations
non random mating
small population
what are the mechanisms of microevolution: (5)
bottleneck effect
mating and sexual reproduction
mutation
gene flow
natural selection
what is the bottleneck effect and founder effect
theres a large population that becomes a small population because of:
a natural disaster
a small group breaks off to form a new population
this forms a new population which might have a completely different allele frequency that the original population → this is changes in allele frequency = microevolution
explain how mating and sexual reproduction is a mechanism for microevolution
non random mating (selects more desirable traits) and secual reproduction introduce new genetic combinations into a population → this creates changes in the allele frequency which is microevolution
explain how mutation is a mechanism of microevolution
random changes to the nucelotide sequence can cause a new trait/ aka allele to occur which can change the allele frequency of the population (if beneficial) = microevolution
explain how gene flow is a mechanism of microevolution
gene flow is the immigration of new genes (it can happen when new populations immigrate)
new organisms into a population can change the allele frequency resulting in microevolution
how is natural selection the “ultimate” determiner of microevolution
in other words how would it differ from the other 4 mechanisms of microevolution?
the other 4 mechanisms of microevolution: sexual reproduction, mutation, gene flow and bottleneck/founder effect produce VARIATIONS that are beneficial to the organism and increase their changes of reproducing and surviving in THAT specific environment
however natural selection is the only mechanism that creates adaptation
how does natural selection create adaptations?
through determining what genes are fit to be passed on in a specific environment
what is darwinian fitness?
components of darwinian fitness (4)
it is how does natural selection determine what genes are fit to be passed on:
genes are fit to be passed on when they are successful in helping an organism be successful reproductively and pass its genes onto the next generation
components:
ability to attract a mate
ability to accomplish mating
ability to produce fertile offspring
ability to raise young to the age of mating
ability to attract a mate:
biologically
physiology
behaviourally
Biologically: colours, symmetry
Physiology: smell, pheremones
Behaviourally: songs, dances, words, “dating”
ability to accomplish mating
Biologically: correct body parts to perform mating
Physiology: make gametes that can fertilize one another
Behaviourally: know how to accomplish mating
ability to produce mature fertile offspring
Biologically: gametes fuse to produce a viable zygote, embryo and newborn
Physiology: allow fetus to develop inside of body or create a self-sustaining egg...
Behaviourally: tailor behaviour for benefit of fetus, incubate eggs
ability to raise young to age of maturity
Biologically: able to give birth and carry young/care for
Physiology: can make milk, has hormones to maintain parenting
Behaviourally: defending young, teaching young to survive
are there different types of natural selection? why?
microevolutionary changes can lead to different types of natural selection:
stabilizing selection: favors intermediate traits, reduces variation and maintains the status quo (ex. human birth weight)
directional selection: favors traits at one extreme of a distribution leading to a shift in the allele frequency of a population overtime
diversifying selection: favors traits at both extremes of allele distribution and intermediates are less likely to survive (ex. darker and lighter shells are better camoflagued compared to intermediates)
what is sexual selection
In biology, sexual selection is a form of natural selection where individuals with certain traits have a higher reproductive success than others due to their ability to attract mates or compete with rivals. It can be driven by two main processes: intrasexual selection (competition within the same sex) and intersexual selection (mate choice by one sex).
there are 2 main reasons why members of one sex need to be selected:
the members of one sex are attracted to specific traits of the other sex, these traits show darwinian fitness
the members of one sex need to outcompete the other members to reproduce
why is sexual selection different from regular natural selection types
natural selection = survival oriented (improves the individuals chances of surviving and reproducing in an environment)
sexual selection = increases the individuals ability to attract a mate and reproduce only!
Natural selection can lead to traits that improve survival and overall fitness, while sexual selection can lead to traits that are primarily beneficial for mating, even if they compromise survival.
how could sexual selection compromise individuals survival
Can lead to exaggerated traits (like huge tails or loud calls) that don’t help with survival and might even be risky — but improve chances of reproducing.
what is it called when sexual selection results in differences between the appearances of males and females
sexual dimorphism
this is when there are distinct differences in size or appearance between the sexes of an animal
types of sexual selection (2)
male male competition (intrasexual selection):
Members of the same sex compete with each other for access to mates.
Often involves male-male competition for dominance or territory.
this happens when resources are concentrated, so there is an aspect of territory and using access to resources to attract mates
Traits selected: size, strength, aggression, antlers, etc.
female choice (intersexual selection):
when resources are dispersed and mates could be anywhere
One sex chooses a mate based on specific traits.
Often females choose males with showy, impressive features or behaviors. → show that they are the healthiest and most attentive mates
Traits selected: bright colors, long tails, complex songs, dancing, etc.
what is artificial selection
when humans make choices that lead to microevolutionary changes, in other words, humans artificially select what traits a population should have
hardy weinberg principle → law of genetic equilibrium
The Hardy-Weinberg Principle is a mathematical model used to study how populations evolve (or don’t) over time.
📌 Key Idea:
If certain conditions are met, the frequency of alleles and genotypes in a population will remain constant over generations.
This means the population is not evolving — it is in genetic equilibrium.
conditions for no evolution/ genetic equilibrium:
No mutations
No natural selection
Large population size
No migration (gene flow)
Random mating
why are hardy weinberg equations important
Used as a baseline: If a population doesn’t match Hardy-Weinberg predictions, it means evolutionary forces are acting on it.
It helps scientists detect natural selection, mutations, or gene flow in real populations.
define macroevolution
macroevolution is an evolutionary change that causes a speciation event which is the formation of a new species
mechanisms for macroevolution (how do these these large scale changes occur?)
gradually → compounded microevolutionary changes which results in big differences between a species and their ancestors until they are unable to mate → forms new species = macroevolution
abruptly → environmental pressures (like volacno eruption, meteor etc.) cause rapid natural selection
a) what is polyploidy
b) how is polyploidy connected to macroevolution and the formation of a new species?
a) when an organism ends up with an extra set of chromosomes usually due to an error in meiosis, so instead of halving the chromosome number the cell accidentally duplicates it
b) because polyploidy organisms have a different number of chromosomes, they usually cant mate successfully with the original species → however if the polyploid can survive and reproduce (either asexualy or with other polyploids) it becomes reproductively isolated → instant speciation called sympatric speciation
why does polyploidly result in fast speciation? (aka abrupt speciation)
there is no need to wait for the gradual accumulation of genetic changes (accumulation of microevolution)
one mutation will result in a new chromosome number and create reproductive isolation
explain the example of speciation in the genus allium (plants) by polyploidy
the genus allium includes monocot flowering plants ex. the onion, garlic, chives, scallion, leeks, shallots
but polyploidly has arose due to chromosome doubling through non-disjunction. this reproductively isolates similar populations which creates many species
what are the benefits of polyploidy in agriculture (4)
Makes the population stronger and healthier by mixing more genes, so there's less risk of inherited diseases.
Adds more genetic variety, giving the population more options to survive changes.
New traits appear more often, helping the population adapt faster and form new species.
Leads to bigger flowers, fruits, or roots in plants.
why is it so hard to tell if things are the same species? (4)
asexual reproduction in some organisms
geographical separation of species that can interbreed
formation of hybrids
sexual dimorphism → some members of the same species look very different
what are the 2 main mechanisms of speciation (aka creating a new species through macroevolution)
allopatric: geographical isolation
sympatric: speciation caused my reproductive isolation within the same geographical area
what is allopatric speciation
when organisms are phsycially separated. memebers of the same species are geographically isolated due to natural or human factors which prevents gene flow between these populations
lack of gene flow results in: mutations being unshared
also natural selection can place different pressures on the separated populations which can result in different mciroevolutionary changes
this can prevent the 2 populations from being able to reproduce even if they are reunited.
sympatric speciation
types (2)
sympactric speciation is when species form due to reproductive isolation within the same geographical location
types:
pre zygotic: prevents the zygote from forming
post zygotic: prevents the organism from fully developping to mature fertile age (reproductive age)
pre-zygotic isolating mechanisms (4)
Behavioural - never mate because they don’t recognize each others courtship rituals
Temporal - different breeding seasons, diurnal vs. nocturnal lifestyles are unlikely to meet and mate
Geographic - live in different niches within the same environment; aquatic vs. terrestrial
Mechanical - prevent mating OR gamete fertilization
post-zygotic isolating mechanisms
Zygote mortality - misscarriage terminates pregnancy due to gamete incompatibility
Hybrid inviability - offspring are weak or don’t survive to age of reproduction
Hybrid infertility - offspring are infertile and cannot reproduce
patterns/trends of speciation (2)
convergent:
different ancestors
analogus structures
becomes more and more similar
divergent:
same ancestor, but they evolved to be different species
homologus structures
becomes more and more different
adaptive radiation
Definition:
Adaptive radiation is when one species rapidly evolves into many new species, each adapted to a different environment or way of life.
Key Points:
Happens when new environments or resources become available.
Species evolve to fill different ecological niches (roles in the environment).
Driven by natural selection — traits that help survival in a niche become more common.
🐦 Example:
Darwin’s finches in the Galápagos Islands:
All evolved from a common ancestor.
Developed different beak shapes to eat different types of food (seeds, insects, etc.).
co-evolution/parallel evolution
essientially when 2 species have a relationship (symbiotic or parasitic) or are closely linked, when one evolves the other will evolve too, this is called parallel evolution between the 2 species.
what is genetic drift? how is it related to the bottleneck/founder effect?
Definition:
Genetic drift is a random change in the frequency of genes in a population, especially in small populations.
Key Points:
Not caused by natural selection — it’s luck-based.
Can cause loss of genetic diversity.
Sometimes, rare traits can become common just by chance.
🎲 Example:
If a natural disaster randomly kills most of a population, the survivors might not represent the original gene pool. This is called a bottleneck effect.
Or when a few individuals start a new population (founder effect), their genes dominate the new group.
what is hybridization?
Hybridization is when individuals from 2 different species or distinct populations interbreed and produce offspring (these are hybrids)
if the hybrids are fertile and can reproduce, hybridization can lead to new gene combinations and sometimes new species → speciation
think ancient humans and neanderthals interbreeding to form modern humans (hybrids)