AP Bio: Unit 7: Evolution

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Charles Darwin

English naturalist whose most notable research was done at the Glapagos Islands.

What was Darwin interested in?

biogeography: the geographic distribution of species

Darwin’s hypothesis:

Organisms left South America and colonized

the Galapagos Islands where they then

diversified and gave rise to a new species

What was Darwin specifically interested in?

Finches

The following questions will be True or False

Practice!

“Natural selection gives organisms what they need to survive”

FALSE: natural selection has no knowledge of what organisms “need.” Natural selection

simply acts on genetic variations that lead to

survival and reproduction

“Natural selection acts for the good of a species”

FALSE: Natural selection has no intentions. It only acts on traits that lead to survival and

reproduction.

Ex: A trait that makes a species the best predator will lead them to eat all their prey → starvation

“Natural selection is a process involving organisms trying to adapt to their surroundings”

FALSE: Natural selection acts on random

mutations that have led to a genetic variation in the population.

“Survival of the fittest” is a common phrase you may have heard. The term “fittest” refers to the organisms in a population that are the strongest, healthiest, and fastest.

FALSE: the fittest organism simply refers to

the organism that (you guessed it) can survive and reproduce

Ex: Organisms with sickle cell anemia are NOT “the healthiest,” but CAN survive malaria.

Back to Definitions!

Learn!

Evolution

Change in the genetic makeup of a population over time; descent with modification

(This definition was proposed by Darwin)

Natural Selection

A process in which individuals that

have certain traits tend to survive and reproduce at higher rates than other individuals because of those traits

Fitness

Ability to survive and reproduce

(Evolutionary fitness is measured by

reproductive success)

What do phenotypes and fitness have to do with each other?

Some phenotypes will increase or decrease an organism’s fitness

biotic

living

abiotic

nonliving

What causes selective pressures to populations?

Environmental change

What affects the rate and direction of evolution?

The fluctuation of biotic and abiotic factors

flip to see the effect

it changed woww

The more genetic diversity in a population…

the better it can respond to changes in the environment

The theory of natural selection is based on two main observations that Darwin made:

1) traits are heritable

2) More offspring are produced than can survive

Traits are heritable

Characteristics can be passed from parent to offspring

More offspring are produced than can survive

This leads to competition for limited resources, which results in differential survival

The traits that lead to survival (“favorable”

traits) will accumulate in the population

Adaptations

inherited characteristics of organisms

that enhance their survival and reproduction

WHAT evolves?

populations evolve, NOT individuals

Artificial Selection

the selective breeding of

domesticated plants and animals to

encourage the occurrence of desirable traits

Natural Selection

Nature “selects” traits that are better suited for survival and reproduction

Artificial Selection

Humans select traits that are desirable

Domestication of plants and animals

Can both natural and artificial selection lead to evolutionary change in an organism?

Yes, but natural selection occurs in nature without the influence of humans

Population

a group of individuals of the same species that live in the same area and interbreed

to produce fertile offspring

Gene pool

a population’s genetic makeup

(consists of all copies of every type of allele)

What is a fixed population?

If the population only has one allele present for a particular locus in the population

Many fixed alleles= less genetic diversity

Locus

The specific, physical location or position of a gene on a chromosome

Microevolution

small scale genetic changes in a population

What RANDOM occurences drive evolution?

Mutations

Genetic Drift

Migration/gene flow

Natural selection

Mutations

*Results in genetic variation

*can form new alleles

can be harmful, neutral, or beneficial. Most mutations are in the neutral to harmful range. Not all mutations lead to evolution.

What is the difference between mutations in eukaryotes and prokaryotes?

Mutation rates tend to be slow in plants and

animals and fast in prokaryotes due to a faster generation time

Genetic drift:

chance events that cause a change

in allele frequency from one generation to the next

*Most significant to small populations

*Can lead to a loss of genetic variation

*Can cause harmful alleles to become fixed

*Does NOT produce adaptations

What are the two types of genetic drift?

Bottleneck effect

Founder effect

Bottleneck effect

when a large population is

drastically reduced by a non-selective disaster.

(some alleles may become overrepresented, underrepresented, or absent).

Ex: Flood, famine, hunting, etc.

Founder effect

when a few individuals become isolated from

a large population and establish a new small

population with a gene pool that differs from the large population

(loses genetic diversity)

Gene flow

the transfer of alleles into or out of a

population due to fertile individuals or gametes

(alleles can be transferred between populations)

Ex: pollen being blown to a new location

AGAIN, what is reproductive success measured by?

Relative fitness: The number of surviving offspring that an individual produces compared to the number left by others in the population

How can you check the effects of natural selection?

By examining the changes in the mean of phenotypes

What are the three modes of natural selection?

Directional selection

Stabilizing selection

Disruptive selection

Sexual selection

a type of natural selection that

explains why many species have unique/showy traits

(can produce traits that are harmful to survival)

Ex. Colorful feathers in male peacocks makes them easier to spot by predators

Hardy Weinberg Equilibrium

A model used to assess whether natural selection or other factors are causing evolution at a particular locus

Determines what the genetic make up of the

population would be if it were NOT evolving

This is then compared to actual data:

If there are NO differences, then the

population is NOT evolving

If there ARE differences, then the

population MAY BE evolving

The Hardy Weinberg principle states:

The frequencies of alleles and genotypes in a population will remain constant from

generation to generation, provided that only

Mendelian segregation and recombination of

alleles are at work (hypothethical w/ no evolution taking place, irl, allele and genotype freequencies do change over time)

What five conditions must be met to be in Hardy Weinberg Equilibrium?

No mutations

Random mating

No natural selection

Extremely large population size

No gene flow

If the Hardy Weinberg Equilibrium conditions are not met, what happens?

microevolution occurs (mutation, gene flow, genetic drift, natural selection, and non-random mating).

Genetic drift

the random fluctuation of allele frequencies within a population due to chance events, typically reducing genetic variation, especially in small populations.

(tthrough bottleneck or founder effect)

What are the Hardy Weinberg formulas?

Look!

When a question gives “allele frequencies,” what formula do you use?

p+q=1

When a question asks about individual organisms or populations, what formula do you use?

p2+ 2pq+ q2 =1

What should you do first when solving?

Find both p and q first!

What is the difference between genotype

frequencies and allele frequencies in a population?

genotype frequencies refer to how alleles

combine. Allele frequencies refer to an allele’s relative distribution in the population (ie how common is the allele).

Hardy Weinberg equilibrium is often referred to as a null model of evolution. What does this mean?

a null model of evolution is one where no

evolution occurs, which is assumed with Hardy Weinberg if all conditions are met

Is genetic diversity good for survival?

Yes, because the more genetic diversity in a population, the better it can respond to changes in the environment

In contrast, species with low genetic diversity are at risk of decline or extinction

Species

a group able to interbreed and produce

viable, fertile offspring

Speciation

formation of new species

(Results in diversity of life forms)

What has an impact on speciation?

Geography has an impact on speciation

What are the two modes of speciation?

Allopatric speciation

Sympatric speciation

Allopatric speciation

Physical barrier divides population or a small

population is separated from main population.

Populations are geographically isolated

*Prevents gene flow

*Often caused by natural disasters

Sympatric speciation

A new species evolves while still inhabiting

the same geographic region as the ancestral

species.

Usually due to the exploitation of a new niche

Niche

the functional role and position of a species within an ecosystem, encompassing its use of resources (food, water, light) and tolerance for abiotic conditions (temperature, pH). It describes how an organism "makes a living"—where it lives, what it eats, and how it interacts with other organisms.

Why does speciation occur?

because of reproductive isolation

what are the two types of reproductive isolation?

Prezygotic barriers

Postzygotic barriers

(Both types maintain isolation and prevent gene flow between the populations)

Prezygotic barriers:

prevent mating or hinder fertilization

Five types:

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

Gametic isolation

Habitat isolation:

Species live in different areas

or they occupy different habitats within the same area

Temporal isolation:

species breed at different

times of the day, year, or season

Behavioral isolation:

unique behavioral patterns

and rituals separate species

Mechanical isolation:

the reproductive anatomy of one species does not fit with the anatomy of another species

Gametic isolation:

proteins on the surface of

gametes do not allow for the egg and sperm to fuse

Postzygotic barriers:

prevent a hybrid zygote from developing into a viable, fertile adult

Three types:

Reduced hybrid viability

Reduced hybrid fertility

Hybrid breakdown

Reduced hybrid viability:

The genes of different

parent species may interact in ways that impair the hybrid’s development or survival

Example: domestic sheep can fertilize

domestic goats, but the hybrid embryo dies

early on

Reduced hybrid fertility:

a hybrid can develop into a healthy adult, but it is sterile.

Usually results due to differences in number of chromosomes between parents

Example: a male donkey and a female horse

can mate to produce a mule, but mules are

sterile

Hybrid breakdown:

the hybrid of the first generation may be fertile, but when they mate with a parent species or one another, their offspring will be sterile

Example: farmers have tried crossing different types of cotton plants, but after the first generation the plants do not produce viable seeds

What is speciation a bridge of?

The concepts of microevolution and macroevolution

Microevolution:

change in allele frequencies within a single species or population (natural and sexual selection, genetic drift, gene flow)

Macroevolution:

large evolutionary patterns

(adaptive radiation, mass extinction)

Stasis

no change over long periods of time

Punctuated equilibrium:

when evolution occurs rapidly after a long period of stasis

Gradualism:

when evolution occurs slowly

over hundreds, thousands, or millions of years

Divergent evolution:

groups with the same common ancestor evolve and accumulate differences resulting in the formation of a new species

Adaptive radiation:

if a new habitat or niche becomes available, species can diversify rapidly

Convergent evolution:

two different species develop similar traits despite having different ancestors

*Analogous traits

Extinction:

the termination of a species

How many mass extinctions have occurred throughout the Earth’s history?

5 mass extinctions

What things can affect extinction rates?

*Human activity

*Ecological stress —> extinction rates can quicken

What happens if a species goes extinct?

A new niche opens up (like they lost their job, so someone else is replacing them) and it can be exploited by a different species.

What are the primary sources of evidence for the theory of evolution?

The fossil record

Comparative morphology

Biogeography

Fossils:

remains or traces of past organisms

Fossil record:

gives a visual of evolutionary change over time

Fossils can be dated by examining the rate of carbon 14 decay and the age of rocks where the fossils are found

Gives geographical data for the organisms found

Comparative morphology:

analysis of the structures

of living and extinct organisms

Homology:

characteristics in related species that

have similarities even if the functions differ

Embryonic homology:

many species have similar

embryonic development

Vestigial structures:

structures that are conserved even though they no longer have a use

Example: tailbone and appendix in humans

Molecular homology:

many species share similar DNA and amino acid sequences

Homologous structures:

characteristics that are similar in two species

because they share a common ancestor

Example: arm bones of many species

Convergent evolution:

similar adaptations that have evolved in distantly related organisms due to

similar environments