Early Earth & Geologic Time

3 eons Phanerozoic (present-542 mya)

Proterozoic ( 542 mya- 2500 mya)

Archaean (2500 mya-4600mya)

Phanerozoic Era

Divided into eras, periods and epocs Cenozoic era (present-65.5 mya)

includes 4o and 3o periods. Adaptive radiation of mammals, insects and

birds. Emergence of woodland and grassland. Evolution of humans. Possible extinction underway

Mesozoic era (65.5 mya- 251 mya) Cretaceous, Jurassic, and Triassic

periods (3 major mass extinctions) Appearance and extinction of dinosaurs. Appearance of turtles, small mammals,

gymnosperms, and ferns. Pangea broke up (continental drift) Climate warming.

Paleonzolic Era (251 mya-542 mya) 3 major extinctions as well.. Emergence of marine animals. Radiation of marine invertebrate Land plants Diversification of insects, amphibians,

and reptiles. Oceans formed at the end.

Proterozoic Eon

Atmospheric accumulation of O2. Origin of eukaryotic cells

Archaean Eon

Earth’s crust formed Atmosphere First seas First prokaryotes

Organic Compounds & First Cells 13-15 bya: universe formed 4 bya: Earth formed

First atm Earth crust and first seas molecular evolution protocell prokaryote eukaryote

Clay hypothesis

A.a. stuck to clay, forming proteins when energized by the sun.

A.a. could have bonded to form proteins near the deep-sea hydrothermal vents.

Both support the idea that protein enzymes need to be in place before any other chem. Rxn like replication or metabolism can take place

RNA first hypothesis

RNA in the form of ribozymes, can act like enzymes that are needed for protein synthesis and would therefore precede protein and DNA systems.

Formation of first cells

A.a form long chains of proteins Fatty acid and alcohols will form sacs

around clay. Proteins + lipids + water =

membrane-like structure similar to the phospholipid bilayer membrane of cells.

Lead to protocells (could replicate) first prokaryote.

Organizing Information About Species

19.4-Comparing DNA and Proteins Kinds and numbers of biochemical

similarities among species reflect evolutionary relationships

DNA and amino acid sequence differences are greatest among lineages that diverged long ago, and less among recently diverged lineages

Remember that…

1. Mutations are random and can occur anywhere on the DNA

2. Most mutations are neutral3. Neutral mutations help to identify

when lineages diverge4. Correlating changes in DNA with

morphological changes in fossil record can help correlate common lineages

5. Essential genes (cytochrome B) are more guarded = harder to mutate

Cytochrome C= federal reserve

Molecular Comparison:

A.a. sequence comparison can be used to determine species relationships.

Single substitution may have large or small effects based on the amino acid that is replaced and what it is replaced with.

Mitochondrial DNA= used to determine familiar relationships because it is passed down without the effects of crossing over (mom’s side)

Making Data into Trees

Parsimony analysis; determines the most logical connections between species.

Rule of cladistics: simplicity guides relationships, the closer a relationship amongst species, the least amount of difference

Evolutionary trees with the fewest differences are more likely to be correct.

Platypus ancestry www.nature.com/news/2008/080507/full/453138a.html

Individuals don’t evolve-populations do Genetic variation exists amongst

population, but they also hold certain morphological, physiological and behavioral traits on common

Gene Pool

All of the genes in the entire population constitute the gene pool

Each gene exists in tow or more slightly different molecular forms called alleles, which offspring inherit and express as phenotypes (Aa)

Dimorphism: two variation of a trait in a population

Polymorphism: 3 or more variations of a trait. Offsprings inherit genotypes NOT phenotypes.

Environmental phenotypes are caused by adaptation and therefore are NOT inherited.

Mutations Revisited

HERITABLE changed in DNA that can alter gene expression

Random= neutral, beneficial, harmful or lethal depending on other interactions.

THE ONLY SOURCE OF NEW ALLELES- the genetic foundation for biological diversity.

HARMFUL, BENEFICIAL, NEUTRAL OR LETHAL?

Harmful, beneficial, neutral, lethal?

Stability and Change in Allele Frequencies

Measure of abundance of each kind of allele in the entire population

Change in allele frequency= evolution (shift in the genetic equilibrium)

Hardy-Weinberg rule (coming up!!)

Stable populations

1. no mutation are occurring2. The population is very, very large3. Population is isolated from other

populations of the same species4. All members survive, mate, and

reproduce ( no selection)5. Mating is random

Microevolution

Change in frequency brought on by Mutation Genetic drift Gene flow Natural selection

Small scale changes in allele’s frequency prevent genetic equilibrium

A population in equilibrium

Natural Selection

Most influential microevolutionary process

An allele that ensure better survival will influence frequency.

3 major categories of selection Directional Stabilizing Disruptive

Directional selection

Shifts allele frequencies in a consistent direction. Traits at one end of the

freq. becomes more and more prominent.

In response to environmental pressures.

As a new mutation appears and is adaptive.

E.g.: Pocket Mice

Habitat: Arizona desert.

Light colored fur blend in with the granite.

Smaller pop’n w/ darker coat blends in with dark basalt.

Selective Pressure?

Resistance in Antibiotics

A typical two-week course of antibiotics can exert selection pressure on over a thousand generations of bacteria

Antibiotic resistant strains are now found in hospitals and schools

Stabilizing Selection

Favors the most common phenotype in the population

Weaver birds in the African savanna. Body weight is a tradeoff between

the risks of starvation and predation. Leaner birds vs. fatter birds? Pros and cons….which trade wins?

Disruptive Selection

Favors forms at the extremes of the phenotypic range.

African finches have either large or small sized beaks. No in between.

Smaller billed birds fed on soft seeds. Larger billed birds fed on harder

seeds.

Show animations now Stabilizing selection Disruptive selection Adaptation to what Change in moth population African finches

Maintaining Variation in Population Sexual Selection

Most males of a specie are larger, more colorful, more aggressive or have a special courtship behavior. Sometimes these traits are maladaptive.

Based on any trait that gives a competitive edge in mating.

Balanced polymorphism

Humans that are homozygous for sickle-cell anemia (Hbs/Hbs) develop the disease and die at an early age.

Individuals with alleles for both normal hemoglobin (Hba) and sickle-cell hemoglobin (Hbs) have the greatest chances of surviving malaria.

Sickle-cell allele persists in the pop’n despite its relative disadvantage.

Genetic drift

Random fluctuation in allele frequencies over time, DUE TO CHANCE ALONE.

May lead to a homozygous condition Occurs faster in smaller populations. One kind of allele remains at a specified

locus in a population. (fixation)

Bottleneck vs. Founder Effect

Stressful situation reduces pop’n size, leaving few ind. to reestablish the pop’n.

This bottleneck decreases the genetic diversity and can be a cause of genetic drift

Few ind. (carrying genes that may or may not be typical of the whole population) leave the original population to establish a new one.

Diversity is limited, random effect of drift.

An example of a bottleneck:Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

Founder effectsA founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have:

reduced genetic variation from the original population. a non-random sample of the genes in the original population. For example, the Afrikaner population of Dutch settlers in South Africa is

descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency. This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.

Inbreeding

Ellis-van Creveld Syndrome

Breeding or mating between close relatives who share a large number of alleles

Example: Old Order Amish in Lancaster County, Pennsylvania (Ellis-van Creveld syndrome

It involves numerous anomalies including post-axial polydactyly, congenital heart defects (most commonly an atrial septal defect producing a common atrium, occurring in 60% of affected individuals), pre-natal tooth eruption, fingernail dysplasia, short-limbed dwarfism, short ribs, cleft palate, and malformation of the wrist bones (fusion of the hamate and capitate bones).

Gene Flow

Genes move with ind. Whey they move out of or into a population.

Microevolutionary process that reduces the effect of mutations, selection, and drift in a population.

Gene flow could lead to genetically modified genes entering a wild population.

Reproductive Isolation

Speciation: evolutionary process by which new species are formed.

Reproductive isolation is necessary for speciation to occur, hence necessary for evolution. The end of gene exchange between

populations The beginning of speciation.

The wood frog and leopard frog have different peaks of mating activity, this prevents any interbreeding.

Behavioral Isolation:Behavioral Isolation is when two populations, because of facing differing sexual selection pressures, will acquire different mating rituals and behaviors. Some organisms within a population will not breed with another organism if it doesn’t have the same mating rituals. In the birds in the follow picture, the mating ritual in the left differs from the mating ritual on the right, and if a bird (even though they look the same) tries to present the ritual between the two variations, the female will not breed with them.

Show animations Albatross courtship Reproductive isolating mechanisms

Allopatric Speciation

Allopatric Evolution:This is the most basic form of evolution. When a population of organisms is separated by physical barriers, they will face different selection pressures that select for different alleles. Over time, the split population will diverge enough that if the two populations ever crossed paths again, they would be unable to interbreed (or they may breed, but they would produce sterile hybrids, like the liger or mule).

E.g: llamas and camels and vicunas (allopatric)

Peripatric evolution is a form of allopatric evolution, but when one population is significantly smaller than the other.

Peripatric Speciation

Sympatric Speciation

This is when organisms evolve in either overlapping or identical environments. This is very similar to parapatric speciation, which is generally referred to when behavioral sexual isolation occurs. One way in which sympatric evolution occurs is in a rain forest, there are several different environments – for example, the canopy and the ground. A single population of insects may separate into two, with one facing different selection pressures in the canopy while the others face a very different pressure on the ground. There is also the famous (in biology circles) Chiclid fish in Africa.

In three lakes of Africa’s Rift Valley, a member of a family of fish named cichlids has evolved a range of ecologies and sizes unmatched anywhere else. Those lakes are known to have formed no later than 1.5-2 million years ago, and the hundreds of species of fish in those lakes occupy ecological niches, and exhibit biological forms, unheard of elsewhere. (One species specializes in eating the eyes of other fish.) The range is greater than what you might find at a coral reef, and all from a small number of evolutionary starting points.

Macroevolution

Occurs at a much larger scale Includes patterns of change such as one

species giving rise to multiple species, the origin of major groups, and major extinction events

Other patterns of speciation Coevolution: caused by ecological

interactions like predator-prey Stasis: long term lineage with relatively

little evolutionary change (a lot of reptile lineages)

Exaptation: appearance of a trait that was originally used for something else (feathers in birds and dinosaurs)

Extinction: fossil records indicate more that 20 mass extinctins. Each one followed by a period of adaptive radiation.