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Evolution, Hardy-Weinberg Law, and the Origin of Life

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Katy Bailon

on 2 May 2013

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Transcript of Evolution, Hardy-Weinberg Law, and the Origin of Life

EVOLUTION Evolution is a genetic change in the population over generations. This descent with modification explains the unity and diversity of related species, and how organisms match their environment.
Evolution can be explained by natural selection= the process in which individuals who have advantageous heritable traits, survive and reproduce more than those without those traits. This is related to adaptation where inherited traits of organism enhance survival for a given environment. NATURAL SELECTION Natural Selection can increase the match between organisms and their environment
It may give rise to adaptation if an environment is changed, or organisms move to a different environment.This sometimes creates new species.
Requirements: overproduction of offspring, competition, genetic variation, some variation that increases chance to survive and reproduce.
*A trait that is advantageous to one environment may not be favorable in another. Artificial selection: selecting and breeding organisms such as crops or pets so that they do not look like their wild ancestors.
Gradualism: species changes very slowly with tiny changes until changes accumulate into a new species
Punctuated Equilibrium: species stay unchanged for a long time, then change quickly creating a new species (due to drastic environmental changes) Direct Observation
Fossil Record
Biogeography 4 types of data that document evolution patterns Direct Observation When organisms have been seen to change over time as their environment changed to better adapted forms. Example: insects have adapted to eat new plant sources that have been introduced into their environment. Example: antibiotic resistant bacteria= as antibiotic use increases the percentage of bacteria that have antibiotic resistances has increased. Homology homologous structure=variation on a structural theme that was present in a common ancestor Fossil Records Fossil records show the differences and similarities between old and present species, and the time in which a group came into existence.
To determine age scientists use radiometric dating: in which a parent isotope decays to a daughter isotope. Measured by the isotopes half-life: the time required for half the parent isotope to decay.
example: Fossils from cetacean mammals (whales, dolphins, and porpoises) show how they originated from land mammals. This is determined by the changing limb structure that led to their loss of hind limbs and the development of flippers. evolutionary tree= reflects evolutionary relationships. so some homologous traits are shared by a wide variety of groups, while others are more species to a smaller group
example: tetrapods such as frogs, mammals,reptiles,birds.
The diagram shows that mammals are closely related to birds because they share a more recent common ancestor as opposed to a mammal and an amphibian. vestigial structures=remnants of features that had a function in ancestor but not in present organism. Convergent evolution: independent evolution of similar features in different lineages. This explains why distantly related organisms resemble one another.
example: marsupials are a distinct group of mammals known as the eutherians. Some marsupials have eutherian look alikes with superficially similar adaptations such as the sugar-glider and the flying squirrel. Both have traits that are alike but the sugar glider is more closely related to marsupials than the squirrel. They evolved independently but have almost identical environments, so go through adaptations in almost the same way. When species share similar traits because of convergent evolution, it is said to be analogous= not homologous, share similar function but not ancestry biogeography= shows that species tend to be more related the closer they are geographically. It is influenced by factors such as continental drift.
250 million years ago earth's landmass was united as one, then it broke apart. Use biogeography to predict where the fossils of species might be found.

example: Scientists made an evolutionary tree for horses based on anatomical data which showed that horses came 5 million years ago in North America. At that time North and South America were not yet connected so horses could not easily pass between them. Thus they can predict that the oldest horse fossils come from North America The History of Life on Earth Chemical and physical occurrences created the early simplistic cells on earth in stages
1. abiotic (nonliving) synthesis of small organic molecules.
2. Joining of the small molecules into larger molecules (macromolecules)
3. Making these molecules into protocells= droplets with membranes that maintained an internal chemistry different from their external environment.
4. Creating self replicating molecules that eventually gave rise to inheritance. The Haldane-Oparin Hypothesis Miller-Urey experiment Early earth conditions: organic molecules and later enzymes as well accumulated in the oceans. Random collections of organic molecules and enzymes wound up in lipid bubbles called coacervates. Coacervates eventually were able to create own enzymes and formed the protocell Created an apparatus that had gases similar to the primitive atmosphere.
Used sparks as energy supply to mimic lightning
Able to create organic molecules. The First Cell First cells most likely anaerobic heterotrophs. Autotrophs (make own food) were favored later when the resources became scarce.The formation of phototrophs (type of autotroph), created O2 as byproduct. The increased oxygen was toxic to some anaerobic organisms.
Aerobic heterotrophs,however, used the the O2 as a way of respiration to get more energy from food. Created the ozone layer which protected Earth from UV radiation and allowed life to prosper. The First Eukaryotic Cell Endosymbiotic Theory= explains how mitochondria and chloroplasts were once smaller prokaryotic cells that began living in larger cells.The anaerobic prokaryote ingested the aerobic prokaryote but did not digest it, so left the membrane around it.
Larger cell got benefits of aerobic respiration and the inner cell got a safe environment. This led to the creation of the eukaryotic cell. Adaptive/Regional Adaptive Radiations adaptive radiations=periods of evolutionary change in which the groups of organisms form new species whose adaptations allow them to fill in different ecological roles. Developmental Genes: insight into Evolutionary Changes developmental genes:control rate, timing, and spatial pattern in a developing organism
Rate and timing: heterochrony= evolutionary change in rate and time of developmental events which can also alter time of reproductive development.
Spatial pattern: homeotic genes determine features such as where a pair of legs will develop. Hox genes give positional information in an embryo. Artificial Selection Fossil Records show that diversity of life has increased over the last 250 million years. This has been fueled by adaptive radiation. regional adaptive radiations= occurs when organisms colonize new environments with little competition. (example: Hawaiian Islands) Homology= similarities resulting from common ancestry. Related species can have traits that are similar but function differently. Homology Biogeography THE EVOLUTION OF POPULATIONS This section focuses on microevolution: “change in allele frequencies in a population over generations.” Remember: individual organisms DO NOT evolve. THREE main mechanisms can cause microevolution:
1. Natural selection

2. Genetic drift (chance events that change allele frequencies)

3. Genetic flow (transfer of alleles between populations) But only natural selection can improve the match between organisms and their environment. Genetic Variation Between individuals in a population and between different populations, there will be differences in genes.
This is required for evolution Individual differences: differences on the same gene locus (location) Population differences: aka geographic variation, differences in the genetic composition between two groups of the same specie Hardy-Weinberg Principle! This principle describes the gene pool of a population that is not evolving. FIVE conditions must be met to reach the Hardy-Weinberg Equilibrium, at which a population is not evolving. 3 NO’s and 2 YES’s
1. NO mutations. No mistakes may be present in alleles and genes.
2. NO natural selection.
3. NO gene flow. Organisms can’t migrate into or out of the population.
4. YES random mating. This ensures random mixing of gametes.
5. YES very large population size. Large fluctuation of allele frequencies is less likely when population is large It is hard to meet all 5 conditions. They aren’t really met in real life. In our example, we did not reach equilibrium because the population is too small. So why do we care about Hardy-Weinberg? Godfrey Harold Hardy (1877–1947) The numbers we calculate using this law gives us the control group, or what we would expect to occur in a population, if none of the 5 conditions is altered
We can compare the actual alleles and genotypes in a population to the H-W numbers, analyze the conditions that were not met, and find the cause(s) of the changes in the population. Dr. Wilhelm Weinberg (1862-1937) You still don’t get it? On your own time, watch Mr. Roisen explain everything! (11 minutes)

Follow this link ---> http://brightstorm.com/science/biology/evolution/hardy-weinberg/ Genetic Drift Genetic drift is when random events cause allele frequencies to change in a population. Two examples of how genetic drift can have a significant impact on a population:

1.Founder Effect: when a few individuals are isolated from a large population and establishes a new population with a different gene pool.

2.Bottleneck Effect: when sudden changes in the environment like a fire or a drought drastically reduce the population and a few members survive by chance. Directional, Disruptive, and Stabilizing Selection Directional Selection: when conditions favor ONE extreme of a phenotype and shifts the population’s frequency curve in one direction.
Disruptive Selection: when conditions favor BOTH extremes of a phenotype, but not the intermediate phenotype.
Stabilizing Selection: when conditions favor NEITHER extremes and instead favor the intermediate phenotype. Sexual Selection Individuals with certain phenotypes are more likely than others to obtain mates.
Can cause sexual dimorphism: difference between two sexes in secondary sexual characteristics.
1. Intrasexual Selection: individuals of one sex compete directly for mates.
EX: Bob and Joe have a fist fight over who gets to date Jane.

2. Intersexual Selection: aka mate choice; when individuals of one sex choose their mates.
EX: female peacocks choose mates with the prettiest feathers Two kinds of sexual selection: THE ORIGIN OF SPECIES This chapter focuses on speciation: how one species splits into two or more species.
But what do we define as a species? The Biological Species Concept This concept states that a species is a group of populations whose members are reproductively compatible and can produce fertile offspring. They CANNOT reproduce with members of other such groups. Reproductive Isolation Biological factors preventing members of two species from interbreeding and producing successful and fertile offspring (hybrids: cross between two species) TWO kinds of barriers: 1. Prezygotic barrier: block fertilization from occurring. 2. Postzygotic barrier: after fertilization is completed and a zygote has formed, errors may kill hybrid embryos, or problems after birth can decrease chances of survival or cause offspring to be infertile Evolution, Hardy-Weinberg Law, and Origin Of Life Chapters 22-25, 26.1-26.3 Taxonomy The discipline of naming and classifying Species Two part formant of the scientific name from a certain organism Binomial Nature The first part of the binomial pertain to the name of the genus, the second part of the binomial pertains to the species within the genus Example:
Panthera pardus (Italicized)
scientific name for a large cat commonly known as the leopard
first letter of a genus is capitalized and the entire binomial italicized Panthera pardus Citations Reece, Jane B., and Neil A. Campbell. "Descent with Modification: A Darwinian View of Life." Campbell biology. 9th ed., International ed. Boston: Benjamin Cummings / Pearson Education, 2011. 452-468. Print. Hierarchical Classification Linking classification and Phylogeny The phylogenetic tree is a branching pattern that matches how taxonomists have classified groups of organisms nested within more inclusive groups But wait...if we take a look at the frequencies we calculated for AA, aa, and Aa, they don't seem to fit with what we observe in the gene pool. It turns out that there are a few rules that must be met for the Hardy-Weinberg Equilibrium to work. Reece, Jane B., and Neil A. Campbell. "The History of Life on Earth ." Campbell biology. 9th ed., International ed. Boston: Benjamin Cummings / Pearson Education, 2011. 507-533. Print. Five Types of Prezygotic Barriers 1. Habitat isolation
2. Temporal isolation
3. Behavioral isolation
4. Mechanical isolation
5. Gametic isolation Reece, Jane B., and Neil A. Campbell. "The Evolution of Populations ." Campbell biology. 9th ed., International ed. Boston: Benjamin Cummings / Pearson Education, 2011. 469-487. Print. Reece, Jane B., and Neil A. Campbell. "The Origin of Species ." Campbell biology. 9th ed., International ed. Boston: Benjamin Cummings / Pearson Education, 2011. 488-506. Print. Habitat isolation: two species rarely, if ever, come in contact because they occupy different habitats, even if not separated by physical barriers. EX: one species of garter snakes live on land, another live in the water, so they won’t mate. Reece, Jane B., and Neil A. Campbell. "Phylogeny and the Tree of Life ." Campbell biology. 9th ed., International ed. Boston: Benjamin Cummings / Pearson Education, 2011. 536-555. Print. Temporal isolation: species that breed at different times of the day, different seasons, or different years cannot mix their gametes. Behavioral isolation: different mating rituals and other unique behaviors prevent different species from mating with each other. EX: Some spiders wave their legs around when they want to mate.If they come up to you and do that, you won’t want to mate with them. Mechanical isolation: when the "key" doesn’t fit the "lock" ;) The PhyloCode Gametic isolation: sperm is unable to fertilize the egg even if sexual interactions occurred. Three Types of Postzygotic Barriers 1. Reduced hybrid viability

2. Reduced hybrid fertility

3. Hybrid breakdown Is the system where all the organism are classified based on their evolutionary relationships Reduced hybrid viability: hybrid dies before birth or unable to survive on its own after birth Reduced hybrid fertility: hybrid cannot mate and/or produce offspring of it’s own. Hybrid breakdown: first generation hybrids are viable and fertile, but when they reproduce again, with hybrids or either parent species, their offspring are not viable or fertile. Hubba hubba! Phyletic vs Divergent Speciation
phyletic speciation: when characteristics of a species change gradually over many generations until the descendants become so different that they are called a new species. divergent speciation: when parts of a species develop into another due to differences in conditions. Divided into allopatric speciation and sympatric speciation. Allopatric Speciation: When two populations get physically separated and become two different species. Sympatric Speciation: Within the same physical location, a few mutations or changes result in the appearance of a new species. More common with plants than with animals. Picture of Harold Hardy: http://www.oocities.org/mathladies/bios/hardy.html Picture of Wilhelm Weinberg: http://comp.uark.edu/~wetges/HWequilibrium.htm Pictures of birds, spider, and mule: Microsoft Word Clip Art Watch this video from 6:34 to 8:23 for an explanation of polyploidy in plants: http://www.brightstorm.com/science/biology/evolution/speciation/ The order of the way Linnaeus place the way people organized the different species. Family, orders, classes, phyla , kingdoms, and domains The Phylogenetic Tree A phylogenetic tree represents an hypothesis about evolutionary relationships.
Depicted as DICHOTOMIES, or two way branch points
it represents the divergence of to evolutionary lineages from a common ancestor Most phylogenetic trees are rooted, which means that the branch point of the tree represents the most common ancestor of all the taxa in the tree.

Basal Taxon: refers to the lineage that diverges early in the history of the group, it lies on a branch that originates near a common ancestor of the group

Polytomy: a branch point from which two or more descendants groups emerge.

Polytomy signifies that evolutionary relationship among the taxa are not yet clear Summarization of the phylogenetic trees
1). They intend to show pattern of descent, not phenotypic similarity. *note: that closely related organism often resemble one another but they might have evolved at different times
** example is crocodiles because they may have resemble 1izards but that doesn’t mean they are closely related to them. They are more closely related to birds but morphology has changed the bird lineage
2). The sequence of the branching in a tree doesn’t necessarily mean that the actual/age is absolute.
diagrams display the phylogenetic tree must have dates of when each species came to be or when they diverged from the main( stream) species.
NOTE: ( from book) unless given specific information about what the branch lengths in a phylogenetic tree mean --- for example that they proportional to time we should interpret the diagram solely in term of pattern of descent
3). We should not assume that a taxon on phylogenetic tree evolved from the taxon next to it What we can and cannot learn from Phylogenetic trees Phenotypic and genetic similarities are due to shared ancestry are called homologies.

Genes and other DNA sequences are homologous if they descend from sequences carried by a common ancestor with same bone structure.

Example of morphological homology
•Organisms that share similar morphologies or similar DNA are more likely to be closely related to species that have very different structures. Morphological and molecular Homologies Convergent evolution occurs when similar environmental pressures and natural selection produce similar adaptations in organisms from different evolutionary lineages

Analogous structures are also called homoplasies (from the Greek word “to mold the same way”)
Fossil evidence help distinguish the difference between homology and analogy
The more similar that two complex structures are the more they are likely to have a common ancestor

If genes in two organism share many portion of their nucleotide sequences it is likely that their genes are homologous Sorting Homology from Analogy Evaluating Molecular Homologies 1st step after sequencing the molecules is to align comparable sequences from the species being studied

If the sequences are related than the nucleotides differ in one or two sites, compared to a species that is not closely related then the nucleotides differ at more than one or two sites Common ancestry is the primary criterion used to classify organisms, using methology to place species in groups called clades.

 Clades include ancestral species and all of its descendants like taxonomic ranks within larger clads. A taxon is equivalent to a clad only if it is monophyletic ( meaning single tribe) it signifies that it consists of an ancestral species and all of its descendants

It contrasts paraphyletic group which consists of an ancestral species but not all. Polyphyletic (many tribes) includes taxa of many different ancestors Cladistics Shared ancestral and shared Derived characters The result of descent with modification has resulted in species sharing some characteristics with their ancestral species and also differ from them

The back bone is a shared ancestral character it originates from an ancestor of the taxon.

Hair is considered a shared derived character an evolutionary novelty unique to a clad
Shared derived characters are unique to particular clades , it should be possible to determine the clad in which each shared derived character first appeared and to use that information to infer evolutionary relationship

An out group is a species of group of species from an evolutionary linage that is know to have diverged before the lineage that includes that species that we are studying ( the ingroup), a suitable outgroup can be determined based on the evidence from morphology, paleontology, embryonic development and gene sequences.

By comparing the ingroup members within each other and with the outgroup, we can determine which characters were derived at various branch points of vertebrate evolution Inferring Phylogenies Using Derived Characters

The principal of maximum parsimony:
We should first investigate the simplest explanation that is consistent with the facts

Principal of Maximum Likelihood:
States that given certain probability rules about hoe DNA sequences change over time Maximun Parismony and Maximum Likelihood Phylogenetic Trees as Hypothesis Phylogenetic hypothesis may be modified when new evidence compels the systematists to revise their trees

An approach know as Phylogenetic Bracketing we can predict the features in two groups of closely related organisms are present in their common ancestor and all of its descendants unless independent data can prove it otherwise DONE!!!!! :) picture of human evolution: commons.wikimedia.org picture of jersey shore: verydemotivational.com picture of bacteria r:http://students.cis.uab.edu/sajayi11/Antibiotic-resistant%20bacteria.html Picture of earth: http://www.astexhibits.com/earth-day-4222013-is-almost-here/ picture from the miller ray experiment www.leap-2010.eu all other photos taken from Pearson Biology
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