Evolution

Evolution

the changes that populations go through over time → leads to biodiversity in populations and species

How does evolution occur?

through changes in allele frequencies

Microevolution

smaller changes in traits within a population overtime

Microevolution processes

• mutation

• natural selection

• gene flow

• genetic drift

Microevolution may (eventually) lead to…

speciation

Macroevolution

major evolutionary changes over along period of time that can lead to new species forming

Macroevolution processes

• speciation

• mass extinction

• adaptive radiation

Phylogeny

evolutionary relationships between organisms

Phylogenetic trees

a diagram used to present evolutionary relationships

Cladistics

classification according to the proportion of measurable characteristics held in common between two organisms

a cladogram is not based on amount of evolutionary change, but instead…

based on shared characteristics

Monophyletic

group of organisms consisting of a single common ancestor and all its descendants - also called a clade

Paraphyletic

group of organisms that consist of a common ancestor and some but not all descendants

polyphyletic

group of organisms that don’t share a recent common ancestor

Formation of molecules

inorganic molecules → organic molecules → monomers → polymers

proteinoids

• amino acid polymers (no peptide bonds)

• formed inorganically through heat + amino acids

• can have some enzymatic activity

• protein-like → possible precursor to cell

Oparin and Haldine Hypothesis

• early earth’s atmosphere was likely reducing

• life arose gradually from inorganic building blocks

• building blocks could form organic compounds from lightning or UV radiaiation

Haldane’s further hypothesis

organic molecules accumulated in the primordial oceans “prebiotic soup”

Miller and Urey Experiment

performed experiment based on Oparine and Haldane hypotheses, with the goal of recreating early Earth conditions

• was successful → good evidence for Oparin and Haldane being correct

RNA World Hypothesis

first form of genetic material to arise was RNA

• versatile

• store genetic info

• can catalyze reactions

• building blocks are easily synthesized

Protocell

• lipid vesicles able to self-assemble

• presence of hydrophilic and hydrophobic molecules could form selectively permeable bilayer

• capable of simple metabolic reactions

Protocell’s were eventually able to…

absorb particles like RNA, not yet cells, but thought to eventually evolve to contain self-replicating molecules with metabolic source

RNA was not initially self-replicating, however…

ribozymes were able to catalyze reactions, this most likely created the possibility of self-replication

Ribozymes eventually…

got absorbed by protocells which created the first cells

RNA can form many shapes, some having advantages…

such as faster and more accurate replication, resulting in more of those molecules (selection event)

RNA to DNA

• easy for changes of RNA to occur

• RNA could be used as a template for DNA nucleotides to be synthesized → allowed for RNA to DNA

RNA to proteins

similar to how RNA → DNA, it went in the opposite direction, have proteins take over as catalysts

first organisms were…

anaerobic heterotrophic prokaryotes

• consumed other organic substances for energy

Autotrophic prokaryotes

• 2nd type of organisms

• formed through mutation of heterotrophic prokaryotes

• created own energy through photosynthesis

• first anaerobic photosynthesizers

• oxygen was by-product

The great oxidation event

the transformation of the earth’s atmosphere → instead of a reducing environment, became an oxidizing environment

Endosymbiotic Theory

Mitochondria and chloroplasts were small individual prokaryotic organisms, engulfed by another prokaryote, formed a symbiotic relationship

Evidence for Endosymbiotic Theory

• circular DNA within mitochondria and chloroplasts

• independent genome

• prokaryotic-like ribosomes

• replicate independently

Paleontological Evidence for Evolution

large, rapid changes observed in fossils show evidence of new species

Embryological Evidence for Evolution

related species = similar development

• relationships reflected in phylogenetic trees and cladograms

Homologous structures → comparative anatomical evidence

anatomical features in species that originate from a common ancestor

• similar physiological structure → may not have same function

Analogous structures → comparative anatomical evidence

anatomical features with similar function but do not share a common ancestor

• points to similar adaptations to similar environments

Vestigial structures

structures that appear useless but had ancestral function

You can analyze different species’ nucleotide and amino acid sequence, you can use these how?

Closely related species have higher percentage of shared sequences

Catastrophism

earth’s history is shaped by major geologic catastrophe

• changes happened because of sudden large violent events over a short period of time

Who’s theory is George Cuvier?

Catastrophism

Gradualism/Uniformitarianism

changes to earth and its organisms happened via small-scale processes, gradually over a long period of time → evolutionarily this would lead to smaller changes over time

Lamarck’s Theory

Inheritance of Acquired characteristics: use and disuse

• acquired traits are passed on

• unused traits deteriorate

• incorrect

• natural tendency towards complexity

Darwin-Wallace Theory

Survival of the fittest

• natural selection (Darwinism)

• Pressure increases fitness - the ability to produce offspring

Descent with modification

• variation present in populations

• lead to a new species

• reproductively advantageous variations (traits) are passed on more frequently

Neo-Darwinism (Synthetic Theory of Evolution)

• genetic mutations produce the variations within a population

• advantageous genes are passed on, not phenotypes

Selection pressures

elements within an environment that prompt organisms to adapt

Resource scarcity

resources are limited, resources do not increase as a population grows larger, thi increases interspecies competition

favorable traits

the individuals possessing these traits get to pass their genes on to the next generation, these traits are adaptations.

Stabilizing selectioin

narrowing the distribution towards the mean → standard curve

• removes extreme variants from population

• most intermediate trait is preserved

Directional Selection

on extreme phenotype is favored over the others

• shift towards one end of the distribution

Disruptive selection

occurs when the intermediate trait is selected against

• environment favors extremes or unusual traits

• shift towards both ends of the distribution

Sexual Selection

differential mating of males and females in a population

• traits that are attractive to the opposite sex can be selected for

• males and females select for different traits in the opposite sex

Sexual dimorphism

difference in appearance between the male and female members of the same species

intrasexual selection

selection within the same sex

• individuals directly compete for mating opportunities with the opposite sex

• usually male behavior

Intersexual selection

Mate choice

• individuals of one sex select for traits in the opposite sex

• usually a female behavior

• commonly appearance-based

fitness

the ability to survive and successfully reproduce

natural selection is driven by…

the inheritance of traits

Overproduction

every species tends to produce more individuals that can survive to maturity

variation

the individuals of a population have many characteristics that differ

Selection

some individuals survive longer and reproduce more than others do

Adaptation

the traits of those individuals that survive and reproduce will become more common in a population

favorability can change depending on…

the surrounding environment

Species in context of evolution

a group of reproductive isolated organisms (can interbreed with one another to produce fertile offspring)

Artificial selection

often favors a specific phenotype

• humans selecting for or against traits through selective breeding

Gene pool

all copies of alleles within a population

Allele

alternative versions of a gene

Allele frequency

how often a certain version of a gene (allele) occurs in a population

ways allele frequencies can be changed

• natural selection

• gene flow

• genetic drift

• non-rando mating

• mutations

Gene flow

the transfer of alleles from population when individuals leave (emigration) or enter (immigration) populations

Genetic Drift

random increase or decrease of alleles by a chance even → smaller the population, the larger the effect

Founder effect - genetic drift

occurs when a small group of individuals become isolated from a larger population

Bottleneck effect - genetic drift

occurs when population undergoes a significant reduction in size due to a natural catstrophe

Non-random mating

individuals choose mates based upon their particular traits

the smaller the population…

the bigger the effect of genetic drift

Sexual selection

choosing mates based on superior traits

mutations

lead to changes in allele frequency

Genetic Variation

differences at the genetic level among members within a population

sources of genetic variation

• mutations

• sexual reproduction

• diploidy

• outbreeding

• balanced polymorphism

Sexual reproduction → increases genetic variation

• crossing over

• dependent upon unique combinations of alleles

• independent assortment

• random fertilization

Diploidy

the presence of two copies of each gene

Outbreeding

mating between individuals who are genetically different

• increases hybrid vigor

hybrid vigor (heterosis)

outbreeding resulting in higher quality offspring than either parent

Balanced polymorphism

maintaining multiple alleles in a population, because having both alleles confers an advantage, therefore they remain in the gene pool

Heterozygous advantage

when heterozygotes have higher fitness than both homozygotes

frequency-dependent selection

fitness of a particular phenotype varies with how common it is

Hardy-Weinberg Equilibrium

Describes a state of genetic equilibrium within a population

• allele and genotype frequencies do not change from generation to generation

• no evolution is occurring

Criteria for Hardy-Weinberg Equilibrium

• no mutations

• random mating

• no natural selection

• large population size → immune to genetic drift essentially

• no gene flow

formulat for hardy weinberg

p² + 2pq + q² = 1

Species

group of individuals which is reproductively isolated, able to interbreed with on another to produce fertile offspring

Reproductive Isolation

When a population is unable to successfully breed (produce fertile, viable offspring) with a related population, they are reproductively isolated

Pre-Zygotic Isolation Mechanisms

before zygote has formed (prevent it from forming)

Habitat Isolation

populations occupy different geographic areas

Temporal Isolation

populations are active and mate at different times

Behavioral Isolation

populations do not perform correct mating behaviors, and are therefore incompatible

Mechanical Isolation

male/female reproductive organs are not compatible

Gametic Isolation

male gamete is unable to fertilize the female gamete

Post-zygotic isolation mechanisms

after zygote has formed

Hybrid Inviability

zygote fails to develop properly and dies before reaching reproductive matruity

Hybrid Sterility

hybrids reach adulthood, but cannot reproduce → are sterile

Hybrid breakdown

hybrids mate and produce offspring, but those offspring cannot reproduce themselves (future generations are inviable)