Unit 7 AP bio

Evolution Definition

Evolution Definition

Genetic change in a species over time, resulting in the development of genetic and phenotypic differences, Individuals do not change

Cuvier’s thoughts on evolution

• believed species didn’t change but he studied fossils

• thought that changes were due to catastrophes and repopulation by species from surrounding areas (called catastrophism)

Lamarck’s thoughts on Evolution

• acquired characteristics could be passed on (so something the individual gained during their lifetime could be passed on, ex. gaining big biceps from working out would be passed on) this is wrong because acquired characteristics do not have a genetic component so they can not be passed down.

• thought that individuals adapt to the environment because organisms strive for perfection

Charles Darwin thoughts on evolution

• believed in natural selection

• traveled for 5 years on the ship The Beagle and wrote “On the Origin of Species”

Natural selection

Organisms that are most fit to their environment will survive and reproduce, passing their genes to the next generation. This causes changes in a population’s characteristics over time as it adapts to the environment. If the environment changes then the characteristics that help it survive change.

3 things need to occur for natural selection:

1. variation must exist (it must be something that can be passed down)

2. organisms must compete for resources (there must be more offspring produced than can survive)

3. Individuals must vary regarding reproductive success (In biology fitness is defined as the ability to reproduce)

Artificial Selection

• human controlled breeding to increase the frequency of desirable traits

• Ex. all dogs were selectively bred for their traits

• chinese cabbage, brussel sprouts, and kohlrabi where all bred from wild mustard

Industrial Melanism

• the color of skin, feathers, or fur acquired by a population of animals living in an industrial region where the environment is soot-darkened

• Ex. peppered moths

Biogeography

• related species that are found in different but neighboring environments are modified for their environment (Ex. galapagos island finches that have different beaks to match their food source)

• supports the common ancestor theory (all the finches descended from a common ancestor with modification)

Fossil evidence for common ancestry

• Fossil record - arrange fossils oldest to most recent to see the progressive change

• radioactive dating - makes fossil record more accurate by calculating the age of a fossil by the amount of a radioactive isotope that has decayed (knowing the half-life)

homologous structures

structures derived from a common ancestor, the structures are anatomically similar even if they serve different functions (Ex. in picture you can sea vertebrate forelimbs). Supports common ancestry

analogous structures

structures that serve the same function but are different because not derived from a common ancestor (Ex. Bird and insect wing are both for flying but do not have similar structures) Not used as evidence for common ancestry

Vestigial structures

structures with no apparent function but resemble structures of a presumed ancestor (Ex. wisdom teeth in humans and hip bones in whales)

development/embryology

similarities in embryo development imply common ancestry

Molecular/biochemical support for common ancestry

• molecular record - comparing DNA sequences or protein structures between species, more similarities means more closely related

• other evidence of common ancestry: is the universal genetic code (the same codons code for the same amino acids), similar structure of ATP, the fact that all organisms have DNA, and many organisms use the same set of developmental genes (developmental genes = Hox or homeobox genes)

Gene Pool

All the genes present in the population but an individual will only have two copies

Alleles

• Alternate versions of the same gene

• some alleles are dominant and some a recessive

• 2 alleles make up a genotype

Allele Frequency

• measures how common each allele is in a population (# with trait/total allele x 100 = % of allele in population)

• can be calculated for each allele in a gene pool

5 Factors that can cause allele frequencies to change (changes in the gene pool)

1. small population (genetic Drift)

2. Non-random mating

3. mutations

4. migration (gene flow)

5. selection

Small population (genetic drift)

• If populations shrink then chance can take over because the gene pool became much smaller (Ex. If 3 red frogs die in a very small population that would decrease the red allele much more than if 3 red frogs die in a much larger population)

• A specific type of genetic drift is called the “founder effect” occurs when a small group of individuals move to a new area and their alleles make up the new gene pool (So if the original population was 10 red frogs and 10 green frogs and 4 red frogs and 1 green frog moves to a new location there is a much higher percentage of frogs that are red)

• Another type of genetic drift is called the “bottleneck effect” where a population becomes suddenly smaller in the same location (often due to humans 🙄)

Non-random mating

• If individuals choose a mate based on factors like location and appearance then that would change the gene pool

• For example, if birds with brown feathers aren’t mated with then the brown feather gene would decrease

mutations

• If a new mutation occurs then the gene pool has changed

• the only factor that introduces new genetic variation into the population that natural selection can act on

migration

• If enough individuals move then that changes the gene frequencies

• this is referred to gene flow

Selection

• this is the only process that leads to adaptation (the rest are random and don’t make changes that makes the organism better adapted to the environment)

• a gene that leads to an advantage will more likely survive and reproduce which will increase the percentage of that gene in the population over time

• acts on phenotypes not genotypes

Macroevolution

• also referred to as speciation because with enough changes a new species can be made

• all species in the world originate from one organism and when species differentiate that is macroevolution

Microevolution

• small changes that might not be visible

• can be observed over short periods of time

• still the same species after the changes

The Hardy Weinberg equilibrium

Describes a population that is not evolving so allele frequencies remain constant from generation to generation if 5 conditions are met:

1. no mutation

2. no migration

3. random mating

4. large population

5. no artificial or natural selection

These are never really met but provide the baseline for the null hypothesis of what a population would look like if it wasn’t evolving.

The Hardy Weinberg Equation

• used to predict allele frequencies in a non-evolving population

• p = frequency of the dominant allele

• q = frequency of the recessive allele

• p² = frequency of homozygous dominant genotype

• 2pq = frequency of heterozygous genotype

• q² = frequency of homozygous recessive genotype

Directional Selection

Occurs when one extreme phenotype has a selective advantage over others so the allele frequency shifts over time in the direction of that phenotype

Stabilization Selection

Occurs when both extremes are selected against which shifts the curve towards the average or median

Disruptive Selection

occurs when the median characteristic is selected and both extremes are advantageous which can lead to speciation if both extremes stop interbreeding

What is a species?

Organisms that can interbreed and produce fertile offspring. (A donkey and horse can breed to reproduce a mule but the mule cannot reproduce so the donkey and horse are separate species)

Speciation

• splitting of one species into two or more species

• The environment is the driving force that creates new species because local populations adapt individually to the demands of their environment which leads to changes in characteristics

• If the populations come back in contact the changes may be big enough that they cannot produce viable, fertile offspring so they have become different species

Reproductive isolation

• this means that gene flow is not occuring

• there are two isolating mechanisms

  1. prezygotic

  2. postzygotic

Prezygotic

• prevent the zygote from forming so prevents reproductive attempts or makes it unlikely that fertilization will be successful if mating does occur. Examples Include:

• habitat isolation

• temporal isolation

• behavioral isolation

• mechanical isolation

• gamete isolation

Temporal isolation

• occurs when two species mate at different times of the year

• Ex. frogs live in the same pond but breed during different seasons

Habitat isolation

• occurs when two species occupy different habitats

• Ex. lions and tigers can potentially interbreed, but usually occupy different habitats

Behavioral isolation

• occurs when two species have different courtship behaviours

• certain groups of birds will only respond to species-specific mating calls

mechanical isolation

• occurs when physical differences prevent two species from mating or pollinating

• Ex. some breeds of dog cannot mate because of differences in size (like a chiwawa and great dane)

gamete isolation

• if gametes of 2 different species meet and they can’t fuse together together to become a zygote

• Ex. molecular incompatibility of egg & sperm (or pollen from different species of plants)

Postzygotic Isolating mechanisms

• these occur after the formation of a zygote. 3 types:

  1. hybrid inviability

  2. hybrid sterility

  3. hybrid breakdown (F2 fitness)

• Hybrid is the offspring of two species

hybrid inviability

• hybrids are produced but fail to develop to reproductive maturity

• certain types of frogs form hybrid tadpoles that die before they become a frog

hybrid sterility

• hybrids fail to produce functional gametes

• mules are sterile hybrids

hybrid breakdown (F2 fitness)

• the first generation (F1) of hybrids are fertile but the second generation (F2) fail to form properly

• the offspring of hybrid copepods have less potential for survival or reproduction

Allopatric Speciation

geographic barriers that physically prevent populations from coming in contact with each other. this isolates the gene pools and is more common

Sympatric speciation

There is no geographic barrier so the populations are still near each other but other factors prevent reproduction between the groups (like microhabitat specialization or polyploidy in plants: Polyploidy is the state of having extra chromosomes which makes it difficult to produce gametes so they can only really self pollinate) Because the gene pools are separated both populations will be affected by the 5 factors that cause changes in the gene pool independently which can result in the formation of new species if the difference is large enough

Adaptive Radiation

• a single ancestral species rapidly gives rise to a variety of new species as each species adapts to a specific environment

• occurs when a group of organisms are the first to arrive to a new environment

• follows mass extinction events in earth’s history

• an example of divergent evolution

• Ex. the galapagos finches were the first birds on the galapagos islands

divergent evolution

• development of new species from common ancestor as species experience different environmental pressures

• species gradually become more different from each other

• homologous structures often come from divergent evolution/adaptive radiation

• aka adaptive radiation

Convergent evolution

• occurs when a biological trait evolves in two unrelated species as a result of exposure to similar environments

• Ex. Dolphin and tuna because they have no recent common ancestor but both have a dorsal fin for swimming.

• analogous structures often come from convergent evolution

Extinction

• all members of a species have disappeared

• naturally occurring but humans have increased the rate

• mass extinction = more than 50% of species on earth disappear

• rates of extinction can be rapid during times of ecological stress like human activity (habitat loss, introduction of exotic/invasive species, pollution, climate change, overexploitation)

• If rate of extinction increases then there will be a loss in diversity in the ecosystem

• extinction provides newly available niches that can then be exploited by different species (adaptive radiation often occurs after a mass extinction event)

• Ex. After dinosaurs went extinct it left space available for mammals to take over

Origin of Life

• earth is about 4.6 billion years old

• evidence of first life is from about 3.5 billion years ago

Hypotheses on how life originated

1. Oparin-Haldane Hypothesis - inorganic compounds, present in Earth’s oxygen lacking atmosphere, combines with an input of energy to form basic building blocks of organic molecules (amino acid, nucleotides, etc.) which become polymers and eventually making cell-like structures

2. Organic molecules came from somewhere else in the universe and was brought to earth through meterioties

3. RNA world hypothesis - RNA was made first

4. Metabolic process developed before the formation of living matter

Miller-Urey Experiment

Showed that it is possible to form organic materials from inorganic materials by replicating early earth conditions (making an atmosphere diatomic oxygen free and inputting an energy source)

Theory of Endosymbiosis

• Prokaryotic cells developed first

• this theory thinks that larger, host cells took in bacteria that had abilities that replicate chloroplasts and mitochondria

• a symbiotic relationship was formed between host and bacteria

2 schools of thought that debate the pace of evolution

1. phyletic gradualism - changes in species occur slowly, gradually over long periods of time

   • we would expect to find fossil evidence of many transitional forms

2. punctuated equilibrium - periods of fairly rapid change followed by long periods of stability with little change

   • fossil evidence follows rapid changes in the environment and we see the before and after not really the transition phases

Diversity of life

• 3-30 million species currently on earth with one 1 million of them named

• taxonomy - the science of classifying and naming organisms

• binomial nomenclature - the two word scientific naming of species in latin where both words are italicized (or underlines if handwritten) and the first word is the genus and the second the species

Levels of Classification

• how species is organized

• from least specific to most specific: Life, Domain, Kingdom, Phylum, Class, Order, Family, Genus, and species

3 domain system

• Current system is the 3 domain system: bacteria, archaea, and eukarya

• Eukarya is further broken down into 4 kingdoms: protist, plants, fungi, and animals

Domain Bacteria

• prokaryotic

• most are heterotrophic (consumers)

• are a few photosynthetic bacteria

• reproduce asexually

• cell walls contain peptidoglycan

• bacteria we encounter on an everyday basis (cause a lot of diseases for humans)

Domain Archaea

• prokaryotic

• some are autotrophs and some heterotrophs

• lack peptidoglycan in cell walls

• thrive in extreme environments like high temperature, high acidity (thermoacidophiles live here), salty areas (halophiles live here) and anaerobic areas

• we do not commonly come in contact with archaea

• genetic material is more similar to humans than bacteria

Domain Eukarya

• all eukaryotic

• some autotrophs and some heterotrophs

• most reproduce sextually but some can produce asexually

• If they have a cell wall it does not contain peptidoglycan

• broken down into four kingdoms:

  1. protists - everything that doesn’t fit into the other kingdoms so can be a variation

  2. fungi - are heterotrophs (decomposers) that can reproduce in both ways and are single and multicellular

  3. plants- all multicellular autotrophic organisms

  4. animals - all heterotrophic, generally reproduce sexually, and are all multicellular