Evolution

EVOLUTIONIB BIO II Van Roekel4/14/14

BILL • What are some examples of evolution you know of? Outline how/why

that evolution took place.• Example: Peppered moths – during industrial revolution, soot covered

the trees, so a species of moths that were once peppered colored became black to blend in to their environment.

Darwin’s Theory of Evolution• Charles Darwin traveled around the world on HMS Beagle for five years making various observations.

• In 1859 Published On the Origin of Species • Came up with the Theory of Evolution by Natural Selection

• Evolution: the process of cumulative change in the heritable characteristics of a population

Evidence for Evolution• Fossil Record: by observing fossils one can conclude that life on Earth is Constantly changing and these changes occur over hundreds of thousands or millions of years.

• Artificial Selection: Small changes over time in domesticated animals by breeders to produce animals with the most desirable characteristics

• Homologous Structures: Similar structures with different functions provide evidence of common ancestors.

Homologous Structures

Structural Evidence con’t.• Vestigial organs

• Organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species

• These do not affect an organism’s ability to survive and reproduce

Embryonic Similarities• Early stages, or embryos, of animals with a backbone are

very similar

• Same groups of embryonic cells develop in the same order and pattern to produce the tissues and organs of all vertebrates

Embryos

Mechanism of Evolution• Overproduction of offspring

• Most organisms produce far more offspring than could survive

• Creates competition for resources in populations (struggle for survival)

• Competition leads to adaptive behaviors to gain/use more resources.

• Leads to variation within species and populations • Variations can provide individuals with advantage or disadvantage for survival

Causes of variety in offspring• Mutations in DNA can lead to harmful or beneficial changes in organisms phenotype• In Each generation only a few genes mutate and most

have little affect on phenotype• Sexual reproduction is more powerful source of variation through meiosis and fertilization• Meiosis: Random distribution of chromosomes results in

each egg and sperm having different combinations from others

• Fertilization: Combination of different genes from sperm and egg cell and only one sperm cell can fertilize one egg cell. Leads to variation in offspring

Natural Selection• Natural selection determines which individuals survive and which do not based on their environment and the compatibility of characteristics to survive.

• AKA Survival of the fittest• Fitness: an individual’s ability to survive and reproduce in a given environment

Process of Natural Selection• Individuals w/in population overproduce offspring,

which have natural variation due to genetic differences• Individuals with poorly adapted characteristics are less

successful at gathering resources and have lower chance of survival

• Individuals with well adapted characteristics are more successful at gathering resources and have a higher chance of survival

• Individuals that survive have a better chance at reproducing and passing on their genetic traits

• Over many generations the accumulations of genetic characteristics in a population results in evolution

Examples: Antibiotic Resistance Bacteria

• Antibiotics are medicines that kill or inhibit growth of bacteria

• Some bacteria can develop resistance to medicine• Occurs when an individual take a course of antibiotics and not all of strain is destroyed

• Remaining bacteria multiply and more are resistant to antibiotics

• Occurs because of mutations, or plasmid transfer (one bacteria donates genetic information to another)

BILL • Evolution is caused by Natural Selection. Outline the process of

natural selection.

• Individuals w/in population overproduce offspring, which have natural variation due to genetic differences

• Individuals with poorly adapted characteristics are less successful at gathering resources and have lower chance of survival

• Individuals with well adapted characteristics are more successful at gathering resources and have a higher chance of survival

• Individuals that survive have a better chance at reproducing and passing on their genetic traits

• Over many generations the accumulations of genetic characteristics in a population results in evolution

Assessment Statements • D.1 Origins of Life on Earth• D.1.1 Describe the process needed for the spontaneous origin of life on

Earth• D.1.2 Outline the experiments of Miller and Urey into the origin of

organic compounds• D.1.3 State that comets may have delivered organic compound to Earth• D.1.4 Discuss possible locations where conditions would have allowed

the synthesis of organic compounds• D.1.5 Outline two properties of RNA that would have allowed it to play a

role in the origin of life• D.1.6 State that living cells may have been preceded by protobionts,

with an internal chemical environment different from their surroundings• D.1.7 Outline the contribution of prokaryotes to the creation of an

oxygen-rich atmosphere• D.1.8 Discuss the endosymbiotic theory for the origin of eukaryotes

Problems for Starting Life1. Life is based on organic molecules, such as amino

acids. 1. Early Earth only had inorganic matter, so either these materials

somehow combined to form organic molecules, or they were extra-terrestrial

2. Organisms must be organized1. Organic molecules must become polymers, larger molecules

necessary for life such as polypeptides (proteins)

3. Living things must reproduce1. Needed self-replicating molecules (RNA is needed to form DNA)

4. Water dissolves molecules1. Living organisms needed to form membranes to separate

internal and external environments

Miller and Urey• Simulated Earth’s believe atmosphere in a lab to see if

they could recreate formation of organic molecules by chemical evolution

• Introduced gases believed to be present at the time (methane, hydrogen, ammonia, water vapor, etc)

• Heated and cooled water to recreate water cycle• Heated water (simulate volcanic activity)• Sparked electricity (lightning)• Exposed “atmosphere” to UV radiation (sun)

Miller and Urey Results• Organic compounds formed!• 13 of naturally occurring 20

amino acids were found• Some sugars and nucleic

acids

• Does not represent life, but now have building blocks of life and know they can be formed from inorganic material

Comets Delivery• Panspermia: idea that life originated on Earth from

materials delivered on a comet in the form of amino acids, or bacteria

• Late Heavy Bombardment: shower of comets 4 billion years ago

• Existing bacteria and archaebacteria have been found in odd and extreme environments, making it feasible that they could survive on comets in space.

Synthesis of Organic Compounds• Several Hypotheses about where synthesis of organic

compounds could have taken place, including:• Space• Volcanoes• Deep Ocean• Intertidal zones with alternating wet/dry environments

Synthesis of Organic Material • Space• Astronomers claim to have found glycine (simple amino

acid) in space• Cosmic radiation could provide energy necessary for

formation of complex compounds• Materials from Mars could have been thrown into space

from comets• Does not prove life originated in space, just that it can

travel through it

Synthesis of Organic Compounds• Volcanoes• Eruptions release water vapor and other gases and

minerals into atmosphere, which could be used to create organic compounds

• Rich source of materials and warm environment are favorable in formation of amino acids

Synthesis of Organic Compounds • Deep Ocean • Hydrothermal vents in deep ocean release hot water from

beneath ocean floor• Hot water rises from earth’s crust, carrying minerals along

the way • Hot bed for strange and ancient creatures, supporting

idea of early life

• http://exploringorigins.org/fattyacids.html

Synthesis of Organic Compounds• Alternating Wet/Dry Zones• Intertidal zones or flood plains have drying clay particles

that could have created catalyzing reactions • When clay dries out and is heated, up to 200 amino acids

can spontaneously join as polypeptide chain. • Stromatolites, one of earth’s oldest life forms, live in

intertidal zones. • Suggests conditions that were favorable for early life

Early Reproduction• Most organisms today pass genetic info using DNA and

enzymes to replicate DNA• PROBLEM!! • Prebiotic Earth had no enzymes, meaning DNA unlikely

hereditary source• What is a likely source that can store, transmit, and

replicate genetic information?• RNA

Early Reproduction• RNA, however, can replicate without the use of enzymes

in some situations.• RNA acts as a catalyst (enzyme) helping certain chemical

reactions occur, such as formation of peptide bonds, polymerization of nucleotides

• RNA acting as an enzyme is called ribozyme• Believe to be genetic material in early earth.

Bill - Review Questions• Outline the Role of clay molecules in the possibility of

creating organic compounds• What is the theory of panspermia • Outline the experiments of Miller and Urey in the origin of

organic compounds.

Review Answers• Organic Molecules Stick to the clay, which can then act as a

catalyst causing organic molecules to be brought together• Panspermia is the theory of the origin of species by the

arrival of organic compounds from space.• Simulated the conditions of pre-biotic earth in a sealed

apparatus. They used gases such as methane, ammonia, water vapor, and hydrogen. Then using boiling water to simulate temperature, electricity to simulate lightning, and uv radiation to simulate the sun, they recreated the conditions of earth to see if organic compounds could form from inorganic compounds. Found organic compounds such as amino acids, sugar, and nucleic acids.

Protobionts• Protobionts: evolutionary precursors to prokaryotic cells• Proteinoid: microsphere, tiny bubble of polypeptide

chains that surrounded polymers, establishing and maintaining different internal environments from the external

• Coacervate: microscopic sphere formed from lipids that formed spontaneously due to hydrophobic forces. Also maintain separate internal environment and are selectively permeable

Protobionts• Protobionts served the purpose of separating internal

environments from external, to protect polynucleotides such as RNA, and allow different chemical reactions to take place

• Over time true cell membranes evolved and other cellular abilities such as respiration and reproduction were developed

Oxygen Production• Remember, no oxygen was present in prebiotic earth,

meaning earliest life forms were anaerobic• Anaerobes consumed food, increased in population, and

eventually food ran scarce• Some bacteria developed a form a chlorophyll allowing

the ability to perform photosynthesis and began producing oxygen (about 3.5 billion years ago)

Importance of Oxygen• Oxygen is toxic to anaerobes, so many were destroyed• Broke down chemicals in atmosphere to carbon dioxide

and oxidized certain sediments• Formed ozone layer, blocking harmful UV radiation

Endosymbiotic Theory• States that organelles found inside modern cells were

once independent prokaryotic cells that were engulfed by a bigger cell. Rather than being digested, they formed a mutualistic relationship with the host

• Supported by the fact that Mitochondria and Chloroplast :• have double membrane• Have own circular DNA (similar to prokaryotes)• Can perform protein synthesis using small ribosomes (prokaryotes)• Can make copies of themselves when more are needed by binary

fission

Review Questions• State the name of one organic monomer and one organic

polymer on prebiotic Earth• Describe one hypothesis of how prebiotic polymers solved

the problem of depolymerization• Explain why UV radiation levels were higher in the

atmosphere of early Earth than they are today. • Outline the theory of Endosymbiosis.

Answers• State the name of one organic monomer and one organic

polymer on prebiotic Earth

• Monomers could be amino acids, simple sugars, or nucleotides

• Polymers could include polypeptide chains, polysaccharides, or RNA

Answers• Describe one hypothesis of how prebiotic polymers solved

the problem of depolymerization

• Surrounds themselves with proetinoid microspheres or coacervates that would protect them from the external environments

Answers• Explain why UV radiation levels were higher in the

atmosphere of early Earth than they are today.

• There was no oxygen present in early earth and consequently, no ozone layer. After oxygen began to be produced by organisms that performed photosynthesis, the formation of the ozone layer began.

Answers• Outline the theory of Endosymbiosis.

• A bacteria cell engulfed another bacterial cell but instead of digesting it, they formed a mutualistic relationship. The smaller cell provided energy to both cells and the larger cell provided protection to the smaller cell.

SPECIES & SPECIATION4/7/14

Assessment Statements • D.2.1 Define allele frequency and gene pool• D.2.2 State that evolution involves a change in allele frequency in

a population’s gene pool over a number of generations• D.2.3 Discuss the term species• D.2.4 Describe three examples of barriers between gene pools• D.2.5 Explain how polyploidy can contribute to speciation• D.2.6 Compare Allopatric and sympatric speciation• D.2.7 Outline the process of adaptive radiation• D.2.8 Compare Convergent and divergent evolution• D.2.9 Discuss ideas of the pace of evolution, including gradualism

and punctuated equilibirium• D.2.10 Describe one example of transient polymorphism• D.2.11 Describe sickle cell anemia as an example of balanced

polymorphism

Gene Pools • Gene Pool: all the genetic information present in the reproducing members of a population at a given time.

• Large gene pools in populations with substantial variety in traits

• Small gene pool in populations with little variation, most notably in cases of inbreeding

Allele Frequency• Allele Frequency measures the proportion of a specific variation of a trait in a population, or the chance a chromosome carries that specific allele• i.e 25% of fruit flies have an allele for white eyes

• Does not mean that that many members of the population have the allele, just that it is present on one of the chromosomes

• What is the allele frequency of A and a in population 1 & 2• ¾ A & ¼ a in population 1 ¾ A & ¼ a in population 2

• How many individuals express the trait coded for by the allele a in population 1 & 2? • O in population 1 and 2 in population 2

Evolution and Alleles• Gene pools are relatively stable over time, however, when

changes occur, evolution is seen • New combinations of alleles lead to new phenotypes, that

can then be selected for or against by the environment • Alleles that are advantageous to a populations survival

will be passed on and have a higher frequency in later generations

• Alleles that are disadvantageous will not be passes on and have a lower frequency in later generations

Evolution and Alleles • Immigrations and

emigrations will also have an effect on allele frequencies

• For whatever reason, when a gene pool in modified, some degree of evolution has occurred.

BILL • What are gene pools? How can you tell evolution occurred by

looking at gene pools? What would cause a change in the gene pool of a species/population?

• Gene pools are all of the genetic information present in the reproducing members of a population at a given time.

• If there is a change in allele frequency (the amount of alleles in a gene pool) then some type of evolution has occurred.

• Alleles that are advantageous to a populations survival will be passed on and have a higher frequency in later generations

• Alleles that are disadvantageous will not be passes on and have a lower frequency in later generations

Species • Species is the basic unit for classifying organisms which included organisms that:• Have similar physiological and morphological characteristics which can be observed and measured

• Have the ability to interbreed and produce fertile offspring

• Genetically distinct from other species• Have common phylogeny

Barriers between Gene Pools• Occasionally, there are barriers between populations of the same species

• Barriers can be:• Geographical Isolation• Temporal Isolation• Behavioral Isolation • Hybridization

Geographical Isolation• Physical barriers such as land or water prevent males and females from find each other and breeding• Rivers• Mountains• Clearing a forest

Temporal Isolation• Incompatible time frames which prevent the populations or gametes from encountering each other• Female parts of flowers of one population mature at a different time from the release of pollen on another population

• One population is still hibernating or has not returned from migrations when another population is ready to mate

Behavioral Isolation• Population’s lifestyle and habits are not compatible with those of another population• Birds rely on courtship displays in order for one sex to mate with the other, if displays of one population are different from another, they will not consider each other for mating

• Hybrids are infertile, so difficult to continue population on their own.

What about Horses and Donkeys?• When they mate, they produce an offspring called a mule.

Why aren’t they the same species?

• Both parents are equines (of the same family) so they are related but are not the same species. They do not posses the same number of chromosomes which is one of the reasons the offspring are infertile.

Questions• Compare and Contrast Geographical and Temporal Isolation• Both are examples of barriers to gene pools but

geographical isolation is a physical barrier such as a mountain or a river whereas temporal isolation is a problem in the synchronization of time when populations try to connect.

• Explain why a zebroid (combination of a zebra and a horse) is not considered a new species.• Because like most hybrids, it is considered infertile and cannot produce offspring.

Speciation• The process of an evolving population changing significantly enough so that the production of offspring with the original population is no longer possible

• Two types of speciation: • Allopatric• Sympatric

Allopatric Speciation• Occurs when a new species forms because it is physically separated from an existing species.

• Gene flow is cut off between these two populations, causing different evolutionary directions

• Once populations have been separated into 2 gene pools they can diverge through natural selection or through random genetic drift.

• http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m3/s2/evm3s2_4.htm

Sympatric Speciation• When a new species forms from an existing species while living in the same geographical area

• Temporal and behavioral isolations could produce a new species

Speciation Activity • You will simulate the process of speciation in a specific

environment • You will work in groups of 3 and will be isolated on a

island that has a specific climate• You must select and write down all the phenotypic

characteristics that exist in your group to improve your group’s survival on the island.

• Answer the questions on the activity on a separate piece of paper (1 per group)

• Draw individual on poster paper• Compare your species to classmates species and answer

questions

Polyploidy• Polyploidy refers to individuals or populations with three or more sets of chromosomes• 3n = triploid• 4n = tetraploid• 5n = pentaploid

• Occurs when cell division does not completely separate copies of chromosomes

Polyploidy• Having multiple sets of chromosomes makes errors more likely to occur during replication.

• Makes polyploidy individuals great source of speciation

• Much more common in plants, which results in more vigorous plants that produce bigger fruits or are more resistant to diseases

Adaptive Radiation• Occurs when many similar but distinct species evolve relatively rapidly from a single or small number of species

• Results in phenotypic (morphological and physiological) adaptations that allow organisms to exploit a different niche in environment

• Examples:• Lemurs• Darwin’s Finches (again)

Adaptive Radiation • Lemurs• Found in Madagascar and Comoro Islands• No competition from apes or monkeys so able to proliferate freely, which led to variation and diversity

• Some adapted for living on ground, others in trees, some live in rainforests, others in deserts, some are nocturnal some are diurnal (day active)

Convergent and Divergent Evolution• What do humans, octopi, and box jelly fish all have in common?

• All have complex camera eyes. These traits evolved independently in organisms that are very distantly related. This is an example of convergent evolution

Convergent and Divergent Evolution• Convergent Evolution

describes the acquisition of the same biological traits in unrelated lineages • Penguins in southern hemisphere

and Auks in Northern hemisphere both have wings as flippers

• Flight in birds, bats, insects and flying fish

• Features that come about as a results of convergent evolution are analogous structures

Convergent and Divergent Evolution• Divergent Evolution is

when two organisms become phenotypically different from a common ancestor because of natural selection

• Features that arise from divergent evolution are called homologous structures. These features either look different or have a different purpose in each species.

Gradualism and Punctuated Equilibrium • Evolutionary biologist believe that pace of evolution may be one of two main ideas:

• Gradualism: changes are small, continuous, and slow

• Punctuated Equilibrium: changes are relatively quick and followed by long periods of little or no change

Gradualism• Supporters argue that the fossil record shows a succession of small changes in phenotypes of species indicating the process of speciation is a steady, constant process with transitional stages between major changes.

Punctuated Equilibrium • Speciation happen quickly, in a response to the environment, i.e. a volcanic eruption that destroys some species. Others then adapt, exploiting new niches made available. The rest of the time, species live for millions of years with little or no change

Problems• Only Evidence available is fossil record• Could be incomplete and missing links are not known

• Some characteristics, such as pigmentation, behavior, or mating calls are not fossilized

• Just because fossilized structures look similar to modern organisms does not guarantee they are direct descendants

BILL • Compare and contrast allopatric speciation and sympatric speciation;

convergent and divergent evolution; gradualism and punctuated equilibrium

• Allopatric speciation occurs when two gene pools are completely cut off from each other by a physical barrier, whereas sympatric speciation occurs when a new species forms from an existing species while living in the same geographical area, most likely because of temporal or behavioral isolation.

• Convergent evolution describes the acquisition of the same biological traits in unrelated lineages and results in analogous structures between unrelated species. Divergent Evolution is when two organisms become phenotypically different from a common ancestor because of natural selection and results in homologous structures between different species.

• Gradualism is the idea that evolution occurs very slowly by small, continuous changes over a long period of time. Punctuated equilibrium is the idea that evolutionary changes are relatively quick and stimulated by some sort of environmental event, which is then followed by long periods of little or no change

Polymorphism• Different versions of a species are referred to as polymorphisms (many shapes) and are typically a result of mutations

• Results in more than one common form of a population

• Transient Polymorphism occurs when the versions change to best fit the environment and these changes can be temporary

• Balanced Polymorphism when two or ore alleles within a population are not changing but are stabilized by natural selection

Transient Polymorphism• Peppered moths have a peppered (grey) and melanic (black) form

• During industrial revolution, melanic form was more prevalent because it provided better camouflage than the grey ones. Called Industrial Melanism.

• Today, because of clean air act and reduced air pollution the population has higher number of peppered moths

Transient Polymorphism & Natural Selection

• In the case of peppered moths, it is natural selection through predation by birds

• Phenotypes are fit or unfit depending on environment

• Black moths more fit when trees covered with soot

• Peppered moths more fit when trees are clean• Survival of fittest

Balance Polymorphism & Sickle Cell Anemia

• Sickle cell anemia can be debilitating, but is also very resistant to malaria.

• Malaria is an infectious disease that occurs in tropical regions where a parasite (Plasmodium) is transmitted to human blood by infected mosquitos

• Parasite attacks red blood cells and causes fever, chills, and possibly death

Balanced Polymorphism & Sickle Cell Anemia

• Polymorphism versions:• Normal RBC (HbAHbA): highly

susceptible to Malaria• Sickle Cell Trait (HbAHbS):

resistant to Malaria due to chemical imbalances (lack of potassium kills Plasmodium), and in most cases are not anemic

• Sickle Cell Anemia (HbSHbs): highly resistant to Malaria, but can be fatal because of curved RBCs and anemia

Balanced Polymorphism & Sickle Cell Anemia

• Allele frequency of HbS (sickle cell) is stable and shows balanced polymorphism because of two pressures of natural selection• Selected against because it can be lethally debilitating• Selected for because it is resistant to malaria

• It can be selected for or against, so balance is reached by heterozygotes, who are more fit to survive in zones plagued by malaria.

Review Questions• Outline the conclusions that Miller and Urey Drew from

their experiments. (2 marks) • Discuss the possible roles of RNA in the origin of life on

prebiotic earth. (4 marks) • Explain the process of speciation (5 marks) • A man with sickle cell trait is climbing the mountains of

Zaire. He has much more difficulty breathing than his fellow climbers. With reference to his genotype and phenotype, explain the reason for this difficulty. (3 marks)

Answers

• Outline the conclusions that Miller and Urey Drew from their experiments. (2 marks)• Organic compounds were formed from inorganic compounds if the

conditions on pre-biotic earth were right. This means that organic compounds could have existed on pre-biotic earth and life may have arisen from non-living conditions.

• Discuss the possible roles of RNA in the origin of life on prebiotic earth. (4 marks) • RNA was thought to be the first genetic material on earth because

it can self-replicate. RNA can act as an enzyme called ribozyme, which has catalytic properties. It can catalyze the formation of RNA by binding amino acids to form polypeptide chains, and it can also be transcribed into DNA using reverse transcriptase.

Answers• Explain the process of speciation (5 marks)

• Process by which one or more species arise from a previous existing population. This occurs as different populations become isolated. Populations can be geographically isolated by physical barriers such as rivers and mountains, or behaviorally isolated by different courtships or habitat preferences. Isolation results in two separate gene pools that will become genetically isolated because of natural selection, which acts independently on the two separated populations. After prolonged isolation, the two species will not be able to interbreed and speciation has occurred.

• Sickle Cell Trait Difficulty (3 marks) • The man has sickle cell trait, so he is a heterozygote, HbAHbS, which

means he has some normal red blood cells and some sickle shaped blood cells which are inefficient for carrying oxygen. Therefore he needs to take larger quantities of air and has more difficulty breathing than others to supply sufficient quantities of oxygen to his cells.