EXAM1 [ch. 18, 19, 20] Flashcards
- broad, well supported explanation with rich predictive value
- based on natural phenomena and causes
- stands up to experimental tests
Scientific theory
- the change in organisms throughout earth’s history
- descent with modification
- a change in genetic composition of a population from generation to generation
- individuals don’t, but populations do
Evolution
Today’s life is different from and descended from earlier life
Descent with modification
- antiquity through 1600’s
- fixed ideal species
- scala naturae (ladder of nature)
Aristotle (384-322 BC)
- botanist
- orderly, nested classification system
- binomial naming
- age of reason (1700’s - 1800’s)
- Father of Taxonomy
Carl Linnaeus (1707-1778)
- geologist
- slow, continuous process ⇒ geological features
- gradualism
James Hutton (1726-1797)
- aka: Father of Geology
- uniformitarianism
- “Principles of Geology” (which was read by Darwin)
Charles Lyell (1797-1875)
- expanded off of Hutton’s ideas
- same geologic processes in past as today
- rate of change today = rate of change in the past
- thus, the earth is very old
Uniformitarianism
- wrote ideas that “forms minute” slowly acquired complexity over time
- Charles Darwin grandfather
Erasmus Darwin (late 1700’s)
- naturalist
- linked evolution to adaptation
- extinct species have been replaced by descendants with new features (these adaptations helped them survive in environment)
- Darwin agreed with these ideas
Jean-Baptiste Lamarck (1744-1829)
an inherited feature that helps an organism’s survival and reproduction in its present environment
Adaptation
- Theory of inheritance of “acquired” characteristics through “use and disuse”
- if an organism changes during life in order to adapt to its environment, the changes are passed to its offspring
- Darwin rejected these ideas
“Lamarckism”
- 1858, wrote to Darwin with same ideas about natural selection from his work in Malay Archipelago
- presented scientific papers on natural selection with Darwin before the Linnean Society
Alfred Wallace (1823-1913)
- naturalist on HMS Beagle (1831-1836)
- travelled mostly to South America (+ Galapagos Islands)
- collected plants, wildlife, fossils
- observed species’ geographic locales and adaptations
- studied local geology
Charles Darwin exploration
- developed evolution theory
- wrote “Origin of Species” in 1859
Charles Darwin
- written by Darwin in 1859
- two main ideas: descent with modification and natural selection
“Origin of Species”
- natural selection is the mechanism for evolution
- heritable variation exists in most species
- all species produce more offspring than the environment can support (based off Mathlthus’s work)
- but, many offspring die off before maturity
[Part 2] Darwin’s Theory: natural selection
- unequal reproductive success among individuals (those with the best traits leave more offspring than others
- those heritable, favorable traits (adaptations) accumulate over vast time, matching the species to its environment
Natural selection inferences
- all present life is related through descent with modification from a common ancestor in the past
- that evolution isn’t a totally new idea
- Earth’s many species are descendants of ancestral species that were different from the present-day species
[Part 1] Darwin’s Theory: Descent with modification
- individuals in a population vary in their heritable characteristics
- organisms produce more offspring than the environment can support
Darwin’s natural selection observations
- individuals that are well suited to their environment tend to leave more offspring
- over time, favorable traits accumulate in the population
Darwin’s natural selection inferences
- explains both diversity & unity of life
- accounts for much of form and function
- can predict outcome of environmental change
- genetic variation is essential/a prerequisite
Theory of Evolution by Natural Selection
antibiotic-resistance in bacteria
Natural selection in action
- origin of life
- how variation works
- how inheritance works
- why variation still exists
- “sudden” changes in fossil record
- source of totally “new” characters
NOT explained in Darwin’s theory
- fossil record
- homology
- convergence
- biogeography
- molecular biology
Evidence of evolution
- forms related by common ancestry
Homology
- structures derived from a common ancestor (but possibly modified for different functions)
- similar structures due to evolutionary origin & based on genetics and developmental origin
-not common structures, but common ancsetor
Homologous Structures
- remnants of ancestral (homologous) structures with no present adaptive function
- ex: blind cave salamanders have eyes (why? because [inference] they descended from a species that could see)
Vestigial structures
- unrelated species have similar adaptations under similar environmental conditions
- _______ evolution: natural selection acted the same way under same conditions (the independent evolution of similar features (analogous) in different lineages)
- ex: torpedo shape for swimming
Convergence
- a result of convergent evolution
- similar functions, but not a common ancestor
- similarities occur because similar selection pressures
- similar phenotypes will evolve in distantly related species due to the same evolutionary pressures
- similar structures due to functional or ecological constraints/pressures and characters can be very similar in appearance due to evolutionary convergence
- ex: white coat (fox & bird)
Analogous Structures
- distribution of species
- corresponds to geographic history
Biogeography
- DNA analysis supports evolution
- closely related organisms have similar DNA
- evolution of new functions for proteins after mutations
- mutation→DNA→segment/DNA sequence→gene→protein(s)
- DNA→mRNA→protein
- the more amino acid sequences shared, the more closely related
Molecular biology
create changes in DNA
Mutations
most diverse (holds basically everything; is 1st in classification system)
[Nested classification system] Domain
most exclusive/specific grouping
[Nested classification system] Species
scientific naming
- GENUS SPECIES
- genus is capitalized
- italicized
- have genus underlined and species underlined but not underlines together!
(- if applicable, subspecies are the absolute most specfic)
Taxonomy
- the science of classifying (or naming) species
- grouping or classifying species together based on similarities and differences (subjective)
Survival of the fittest
- natural selection
- the reproduction of individuals with favorable genetic traits that survived environmental change because of those select traits.
- leads to evolutionary change
Phylogenetic trees
diagrams used to reflect evolutionary relationships among organisms or groups of organisms
Allele
- gene variants that arise by mutation and exist at the same relative location on homologous chromosomes
- one of a number of alternative forms of a DNA sequence at a particular locus
Locus
the specific physical location of a gene on a chromosome
Morphology
the study of the size, shape, and structure of animals, plants, and microbes and of the relationships of their constituent parts
Gene pool
- the sum of all the genes (+alleles) in a population
- many genes have “fixed” alleles (homozygous in all individuals)
- other genes: 2 or more alleles
Zygote
fertilized egg (2n (diploid) = 46)
Fertilization
the union of two gametes (sperm + egg fuse to form a zygote)
Prezygotic barriers
- BLOCKS reproduction
- temporal, habitat, behavioral, gametic, and mechanical isolation
Temporal Isolation
- keeps different species different because of breeding schedules
- prezygotic barrier
Habitat (egological) isolation
- species don’t breed due to distance (they don’t meet)
- prezygotic barrier
Behavioral isolation
- behaviors that impact reproduction
- ex: courtship cues, mating calls/dances/rituals
- prezygotic barrier
Gametic isloation
- sperm of one species might not be able to fertilize an egg from another species (gametes can’t fuse)
- prezygotic barrier
Mechanical isloation
- when mating is impossible due between different animal species due to the incompatibility of their sexual organs
- prezygotic barrier
Postzygotic Barriers
- occurs after a hybrid zygote formation
- hybrid inviability, sterility, and breakdown
Hybrid Inviability
- embryo is formed but can not survive development
- postzygotic barrier
Hybrid sterility
- different species produce viable offspring the can not reproduce
- postzygotic barrier
Hybrid breakdown
- second generation hybrids that can produce
- postzygotic barrier
Strain
a genetic variant within a biological species
What must be true of any organ that is described as vestigial?
it must be homologous to some feature in an ancestor
Niche
Encompasses both physical and environment the organism requires (temperature, terrain) with the interactions it has with other species
Adaptive Radiation
- process where organisms diversify rapidly from an ancestral species into a multitude of new forms due to change in the environment making new resources, niches, etc. available
- because many adaptions evolve from a single point of origin; thus causing the species to radiate into several new ones
Hybrid zones
- may exist during allopatric speciation
- areas where two closely related species interact and interbreed
Fitness
reproductive success and reflects how well an organism is adapted to its environment
With fusion..
..the reproductive barriers weaken and gene flow can occur; hybrids are equally as fit as parents
Sympatric Speciation
- Chromosomal error during cell division
- most common in plants
- speciation occurs in the same geographical area
- other factors create an isolated gene pool
- very rare process (esp. in animals)
Polyploidy
- a condition where a cell or organism has an extra set or extra sets of chromosomes
- results from an error in meiosis, all move to one cell instead of separating
Species
- group of organisms that can interbreed and produce viable, fertile offspring
- not based on similarity of appearance (variation within the same)
Speciation
formation of two species from one original species
A new species arises when..
.. the genetics in two populations become different enough that it prevents gene flow between populations
Gene Flow
the movement of alleles across a species’ range
Biological Species Concept
- organisms that are reproductively isolated from each other are different species
- members of the same biological species share the same gene pool (there is gene flow between two populations)
- are reproductively isolated from other species by natural biological barriers
Morphological Species Concept
- organisms that have significant morphological and anatomical differences are different species
- ex: sorting birds into species based on their wingspans and beak size
Biological reproductive barriers
- Prezygotic
- Postzygotic
How many genes are responsible for reproductive isolation features?
- may be many genes, but could also be as few as one
- ex: variation in one gene keeps 2 snail species from mating (shells spiral in different directions)
- mechanical isolation
Issues with biological species concept
- fossil species
- asexual species
- sometimes hybrids do happen
Allopatric Speciation
- speciation can occur when groups isolated geographically for long time
- physical barrier isolated one population
- not only physical barriers cause speciation: changes (mutations) over time or natural selection, etc. lead to the groups that are no longer reproductively compatible
Dispersal
when a few members of a species move to a new geographical area
Vicariance
when a natural situation arises to physically divide organisms
Possible outcomes of hybrid populations
- reinforcement
- fusion
- stability
(hybrid populations) Reinforcement
- hybrids are less fit than either purebred species
- the species continue to diverge until hybridization can no long occur
- reproductive barriers should be strong
(hybrid populations) Fusion
reproductive barriers weaken until the two species become one
(hybrid populations) Stability
fit hybrids continue to be produced
- hybrids survive or reproduce better then either parents species
Aneuploidy
- results when the gametes have too many or too few chromosomes due to nondisjunction during meiosis
- the resulting offspring will have 2n+1 or 2n-1 chromosomes
Rates of Speciation
- gradual speciation
- punctuated equilibrium
Gradual Speciation
- species diverge gradually through time with small steps
- a rate of speciation
Punctuated equilibrium
- species exhibit a large change in a relatively short period of time followed by long periods of stasis
- a rate of speciation
Population
a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
misconception: Individuals evolve during their lifetimes
Fact: natural selection acts on individuals, but only populations evolve
- genetic variation in population makes evolution possible (variation in heritable traits is a prerequisite for evolution)
- only genetically determined variation can have evolutionary consequences
Phenotypic varation
mostly genetic, but environment can influence expression, creating non-heritable variation
Sources of genetic variation
- new genes and alleles can arise by mutation or gene duplication
- sexual reproduction can result in genetic variation by recombining existing alleles (crossovers, independent assortment, random fertilization)
Genotypic frequency
- % (proportion) of each genotype in the population
- %AA %Aa %aa
- genotype divided by population
Allelic frequency
- % of each allele in the population
- %A allele and %a allele
Microevolution
- a change in allele frequencies in a population over generations
- an evolving population is one that is showing genetic change over generations
Population genetics
the study of what changes the allele frequencies in populations
3 mechanisms that cause allele frequency changes
- natural selection (only causes adaptive evolution)
- genetic drift
- gene flow
Hardy-Weinburg equilibrium
- IF a large population reproduces sexually at random, THEN the genetic frequencies should not change in next generation (remains in equilibrium)
- same frequency of alleles and genotypes in next generation
H-W equilibrium Conditions
- no mutations
- mating is random
- no selection (equal survival)
- very large population size
- no gene flow in or out
H-W Equation
- p + q = 1
- p^2 + 2pq + q^2 = 1
Variables for H-W Equation
- p = freq. dominant allele
- q = freq. recessive allele
- p^2 = freq. of homozygous dominant genotype
- 2pq = freq. of heterozygous genotype
- q^2 = freq. of homozygous recessive genotype
Mechanisms of microevolution
- natural selection
- genetic drift (founder effect, bottleneck effect)
- gene flow
(Mechanisms of microevolution) Natural selection
- acts non-randomly on phenotypes of individuals
- changes allelic and genotypic frequencies of populations non-randomly
- always leads to adaptation of population to current environment
(Mechanisms of microevolution) Genetic drift
- genetic frequency changes due to random events
- often occurs in small populations (ex: sampling errors in stats)
- random changes in allele frequency in either direction
- often reduces genetic diversity
- one allele may become “fixed” (all other alleles lost)
(Mechanisms of microevolution) Founder effect
- a few of one species start new isolated population
- new gene pool differs from original source
- small population size lead to more drift
- better alleles may be lost
(Mechanisms of microevolution) Bottleneck effect
- an event drastically cuts population size
- gene pool of survivors is random; some alleles are lost
- more genetic drift
(Mechanisms of microevolution) Gene flow
- alleles move in/out of population
- includes migration of adults & dispersal of gametes, seeds, larvae
- results to add genetic diversity to population and tends to reduce genetic differences between populations
Outcomes of natural selection on a population depend on?
- relative fitness
- forms of natural selection
- sexual selection
- limitations of natural selection
Relative Fitness
- fitness is relative to other individuals in the population
- “fittest” had the best reproductive success
Forms of natural selection
- Directional selection
- diversifying selection
- stabilizing selection
- frequency-dependent selection
- sexual selection
Directional selection
- form of natural selection
- selects phenotypes at one end of the spectrum of existing variation
- shifts the population’s genetic variance toward the new, fit phenotype
Diversifying selection
- form of natural selection
- intermediates are less fit than extremes
- maintains diversity
- increases genetic variance
Stabilizing selection
- form of natural selection
- intermediate types more fit than extremes
- decreases genetic variance
- higher death rate selects against low birth size, higher death rate selects against large birth size
Frequency-Dependent selection
- form of natural selection
- the fitness of a phenotype depends on how common it is in the population
Sexual selection
- form of natural selection
- success based on traits related to obtaining mates (not directly related to environment)
- leads to sexual dimorphism
Intrasexual selection
individuals of one sex compete directly for mates of the opposite sex
Intersexual selection
also called mate choice, individuals of one sex (usually females) are choosy in selecting their mates from the other sex
Phylogeny
the evolutionary history of a species and its relationship to other species (shown as a tree)
Types of phylogenetic trees
- rooted: single lineage (at base) represents common ancestor
- unrooted: show relationships but not a common ancestor
3 Domains of life
- bacteria (cells do not contain nucleus)
- Archaea (cells do not contain nucleus; they have a different cell wall from bacteria)
- Eukarya (cells do contain a nucleus; include the plants, animals, fungi, and protists)
(rooted phylogenetic tree) Root
indicated that an ancestral lineage gave rise to all organisms on the tree
(rooted phylogenetic tree) Branch point
indicated where two lineages diverged
(rooted phylogenetic tree) basal taxon
a lineage that evolved early and remains unbranched (think outgroup)
(rooted phylogenetic tree) Sister taxa
when two lineages stem from the same branch point
(rooted phylogenetic tree) Polytomy
A branch with more than two lineages
Systematics
the study of phylogenetic relationships
(parts of a phylogenetic tree) Taxon
taxa (plural); group(s) of organisms (species, family, domain, etc. )
(parts of a phylogenetic tree) Clade
a grouping that includes a common ancestor and all the descendants (living and extinct) of that ancestor (monophyletic groups) (ex: all the species on a branch)
Cladistic analysis
- grouping organisms in a way the reflects their evolutionary relationship
- Monophyletic group (clade)
- paraphyletic group
- polyphyletic group
Monophyletic group
consists of an ancestral species and all of its descendants
Paraphyletic group
consists of an ancestral species and some, but not all, of its descendants
Polyphyletic group
consists distantly related species but does not include their most recent common ancestor
Binomial Nomenclature
- aka: specific name
- by Carl Linnaeus (1800’s)
- genus (group) + “specific epithet”
Advantages of phylogenetic classification over Linnaean classification [tree over ladder]
- tells evolutionary history
- does not “rank” organisms and does not suggest that 2 identically ranked groups are comparable
- Linnaean classification “ranks” groups of organisms artificially into kingdoms, phyla, orders, etc.
Cladistics
- method of determining phylogeny or method of hypothesizing relationships among organisms
- analysis depends on characters (anatomical or physiological or behavioral or genetic sequences
Genotype
the genetic constitution of an individual organism
Phenotype
the set of observable characteristics of an individual
Gene duplication
any duplication of a region of DNA that contains a gene
Crossovers
during meiosis, homologous chromosomes trade some of their alleles by crossing over
Independent Assortment
the alleles of two (or more) different genes get sorted into gametes independently by one another (gene variants = alleles)
Fixed allele
an allele that is the only variant that exists from that gene in a population
Homozygote
an individual having 2 identical alleles of a particular gene
Heterozygote
an individual having 2 different alleles of a particular gene
Adaptive evolution
natural selection selects the most beneficial alleles and this increasing their frequency in the population, while it selects against deleterious alleles
Outgroup
a more distantly related group of organisms that serves as a reference group when determining evolutionary relationships of the ingroup
