Founder Effect: When some individuals of a population become isolated. Can affect allele freq of a population
ex. colonizing an island
Genetic Drift
The change in genetic composition of a population due to chance events.
Happens in VERY SMALL populations
Independent Assortment of Chromosomes
(1 Method of Variation)
Occurs during meiosis (metaphase)
Human can have 84 million chromosome combinations from 23 pairs!
Crossing Over
(1 Method of Variation)
Occurs during meiosis (prophase)
Usually happens when matching regions on matching chromosomes break and reconnect to other chromosome.
Meiosis
Cell division. (2n in half=4 gametes)
1. Diploid (2n parent cell) has 2 copies of each chromosome. The pairs of homologous chromosomes (meaning 1 set from each parent) are divided in half to form haploid cells at random. Each haploid cell has genes from mother & father= sister chromatids.
2. Each haploid cell splits in 2, still haploid.They can mature into gametes (a cell that fuses with another during fertilization. Becomes either egg or sperm).
Syngamy
Fertilization process
The fusion of two cells, or of their nuclei, in reproduction.
Result is a zygote
Gene Flow
Migration causes movement of alleles b/w populations
Movement of fertile individuals or gametes
Reduces differences b/w population over time, homogonizing overall genepool.
ex. pollen from plants.
Great Wall of China= Less gene flow across Great Wall than across small mountain path, less gene flow within insect pollinated species than wind pollinated species
Polymorphism
Genetic variation that produces differing characteristics in individuals of the same population or species.
ex. ants in same species but worker, queen & drone all different morphs or forms
The "Biological Species Concept" definition of a Species
Ernst Mayr
Population/ group of populations whose members have the potential to breed in nature & produce viable fertile offspring
(this definition doesn't always work)
Reproductive Isolation
aka Evolutionary Independence: not exchanging biological material.
The existence of biological factors that prevent members of 2 species from producing viable, fertile hybrids
ex. horse+donkey=mule ?
Limitations of the Biological Species Concept
Can't be applied to:
- Asexual organisms
- Fossils
- Organisms whose reproduction is hard to study
Also DNA samples are COSTLY
2 other definitions of Species
1. Morphological Species Concept= If it looks the same, it is the same. Characterizes by body shape, size & other structures.
2. Phylogenetic Species Concept= Independent units. Looks at organisms with unique genetic history.
Limitations with the Morphological Species Concept:
It's easier but not always accurate due to:
a. similarities between species (ex. species of finches)
b. diversity within species (ex. humans)
Cryptic Species
Type of morphospecies. Species that look the same but don't share alleles
ex. copepod looks same here and Japan, but no shared alleles in millions of yrs
The Phylogenetic Species Concept AND Limitations
Can use molecular data, not behavioral, to track movement of alleles & infer lack of gene flow
Applies to all organisms even asexual & fossils
Limitations:
Good methods not available for most organisms (yet)
Very expensive & costly
Summary of Mechanism of Speciation
1. Genetic isolation (allopatric or sympatric)
2. Genetic divergence. Once the genes were isolated from one another they could continue to diverge into a new species through genetic drift and natural and sexual selection
Allopatric ("Other Country") Speciation
*SPECIATION MOST OF THE TIME 99.99%*
Gene flow interrupted or reduced when population is divided into different geographical locations
ex. Hawaiian islands & hundreds of different species of fruit flies
Vicariance
(Form of Allopatric Speciation)
The separation/division of a group by a geographic barrier, like mountain or water
ex. Grand Canyon & different species of chipmunk
Sympatric ("Same Country") Speciation
RARE!
Divergence & speciation without geographic isolation
Difficult b/c genes causing divergence must be linked to or same as those causing reproductive isolation (They are still able to mate, but must choose to not breed together, preferentially)
ex. Fruit flies for Apple trees and Hawthorn trees. Different species, same area. Must lay eggs at different times depending on fruit (host)
Polyploidy (& its 2 levels):
(Results in Sympatric Speciation, plant species)
Extra chromosomes due to accidents during cell division
1. Autopolyploidy: From 1 Species.
Failure of cell division of growing diploid plant after chromosome duplication makes other tissue. Gametes will be diploid.
2. Allopolyploidy: From 2 Species.
A=2n=4. B=2n=6. Meiotic error, 4 chrom +3 =Hybrid w/7 chromosomes. 7 + gamete with 3 =10, even #. Can reproduce w/another 10.
How Seedless fruits are made:
- Female tetraploid (3 chrom) mixed with male diploid (2) produces triploid seeds
- Triploid seeds grow into plants -> produce watermelons
- In Triploid plants- 3 copies of chromosomes can't be divided evenly in meiosis
- Triploid watermelons don't contain mature seeds
Possible outcomes of Secondary Contact
(If species after split run into each other again)
1. Reinforcement
2. Stability
3. Fusion
Secondary Contact (could)= Reinforcement & Stability = Reproductive Isolation. Due to 2 types of barriers...
1. Prezygotic Barriers= Barrier before fertilization
ex. temporal, behavioral, habitat isolations
2. Postzygotic Barriers= Egg fertilized but unsucessful. Prevents hybrid zygote from developing into viable, fertile adult
ex. horse+donkey=mule
Secondary Contact (could)= Hybrids. What happens if no reproductive isolation? Either..
-Hybrid = equal fitness = coalescence (fusion)
-Hybrid = higher fitness = new species
ex. big sagebrush
Macroevolution (definition)
Evolutionary change at or above the level of species
Phylogeny
Is a hypothesis of the evolutionary history of a species or group of related species (the tree!)
How many millions of years ago did plants colonize land?
= 475 Million Years Ago
How long ago did life begin on earth?
= 2.7 to 3.7 BILLION years ago
Systematics
Classifies organisms & determines the evolutionary relationships (the science of making the trees!)
Categories of Classification
(by Carolus Linnaeus)
(Dammit Kitty, Please Come Out For Goodness Sakes!)
The 2-part scientific name of a species is called a:
Binomial
The 1st & 2nd part of the scientific name of a species are:
1st = genus
2nd = epithet
Homo-sapien or Homo-sapien
Evolution (Scientific definition)
A change in the genetic composition of a population over generations
Typological Thinking
Thought original copy w/random errors
Aristotle
Philosophical, not religious
"Historia animalium"- Thought of species as types, behavior as instinctual
Ruled Western biological thinking for over 2,000 yrs
4 Parts of Theory of Special Creation (16th - 19th Century)
1. Linear Progression "The Great Chain of Being" God-Angels-People-Wild Animals-Domestic Animals-Plants
2. Species were created independently of ea.other
3. Species don't change over time..No evolution, no extinction.
4. Species were created recently
Carolus Linnaeus
Founder of taxonomy (classified)
Anti-Evolutionist
Georges Cuvier
French Paleontologist
Believed in catastrophism= Series of large events that reinvented new species
Anti-evolutionist
James Hutton & Charles Lyell
(Hutton & Lyell)
Geologists
Great influence on Darwin
Believed in Gradualism & Uniformitarianism= Gradual processes & same in past & today.
Requires earth much older than biblical account
Jean Baptiste Pierre Lamarck
French Biologist
EVOLUTION (published year Darwin born) 1809
Called "Inheritance of Acquired Characteristics"
1. Use/Disuse- Appendages, organs can change w/use, deteriorate w/disuse
2. Changes are inherited
ex. Giraffe's neck. Mechanism was wrong, but 1st to suggest species could change over time
Epigenetics
Experiences may affect our DNA
ex. environment changing genes like mouse diet affecting agouti gene, affecting fur color, weight, & likeliness to develop cancer
Thomas Malthus
Economist
"Survival of the Fittest"
Believed human growth exponential, food resources limited
Darwin's Voyage on the Beagle
(4 most influential visits)
1. Cape Verde Islands
Rock w/marine shells 45 ft above ground (white sedimentary rock)
Idea: Once underwater. Uniformitarianism & Gradualism began to sink in while reading of Hutton & Lyell.
2. Brazil
Discovered bones of giant ground sloth, armadillos, etc (extinct).
Idea: They were similar to living forms
3. Chile
Andes- Found marine shells at 12,000 ft
Volcanic eruption raised coastal shelf by 8ft.. in ONE DAY
4. Galapagos Islands
Geopgrahpically isolated. Species there for millions of years. Galapagos tortoise: dome-shaped carapace w/low front. Endemic= Species live only in 1 area. Large island w/ low vegetation, don't have predator threat (Santa Cruz, Isabella) Tortoise w/longer neck & front to reach hgher vegetation
"On the Origin of Species" (1859)
Sold out the first day
Convinced leading scientists immediately
What it states:
1. Descent w/modification ("evolved", but only uses term once at end of book)
2. Natural Selection rejected (didn't have proper evidence)
Evidence of (Macro)Evolution (6 Groups):
1. Law of Succession (Fossils of living similar to fossils of extinct)
2. Transitional Fossils
3. Common Ancestors
4. Homology
5. Genetic Code
6. Vestigial Stuctures & Organs
Law of Succession
(Evidence of Evolution at level of species/ Macroevolution)
Fossils in 1 region similar to living organisms in that region
Darwin noted similar pattern in Argentina
ex. Extinct Glyptodont & living Pygmy Armadillo
Transitional Fossils
(Evidence of Evolution at level of species/ Macroevolution)
Used as "missing links"
Dinosaurs -> Birds
Fishes -> Tetrapods
Tetrapods -> Whales
ex. Archaeopteryx= transitional b/w dinosaur & bird. Was reptile with FEATHERS. Germany, 145-150 Million Yrs Ago
Homology (2 Types):
(Evidence of Evolution at level of species/ Macroevolution)
Study of Linkeness
1. Structural Homology
Mammilian forelimbs have same basic structure, even w/different functions.
2. Developmental Homology
Similarities during development, even if different as adults.
ex. human embrios have gills, turn into voicebox & tail remnants
Vestigial Structures & Organs
1. Vestigial Structures: DID have purpose in ancestor. Not costly enough to disappear.
ex. Pelvis bone in whales
2. Vestigial Organs
ex. flightless birds, goosebumps in humans
Convergent Evolution
& Analagous Features
Opposite of Homology
Independent evolution of similar features in different lineages. Resembled features are analogous, not homologous b/c similar function, not ancestry.
ex. flying squirrel & sugar glider = Analagous
3 Principles of Natural Selection
(hint: SAME as principals of Microevolution)
1. Variation w/in a trait
2. Variation is heritable
3. Not all individuals reproduce equally
Lord Kelvin's Theory
(1st Reason why natural selection not easily accepted)
Assumed earth began as molten rock around 7000 degrees F
Knew size of earth & that temp's increase 1 degree for every 50ft of depth
Estimated age of earth as 100 million years old based on equation of heat loss
*This estimate was off b/c Radioactive core made earth constantly heating, not cooling.
Thomas Morgan & Mutation
Refuted idea of no mechanism of novel creation that tried to discredit natural selection
Nobel prize in 1933
Worked w/fruit flies
Previously, mutations were thought to be large, causing speciation
Morgan showed mutation, mechanism, & effect on body
Weissman & "Soft Inheritance"
Weissman: Discredited Lamarckism (acquired characteristics) w/ infamous mouse tail clipping experiment, showing tails chopped don't effect offspring. Inherited characters are from genes of successful parents
Refuted idea of no mechanism of inheritance that tried to discredit natural selection
No mechanism for the creation of novel variation
(2nd Reason why natural selection not easily accepted)
1. Creationism: God creates variation or random imperfections
2. Orthogenesis: Natural tendency towards complexity & perfection w/ humans @ top
3. Transmutationism: Variation in large amounts in short amounts of time
4. Lamarckism: Acquired charachteristics
ex. Giraffe necks
No mechanism for the inheritance of adaptations (3rd Reason why natural selection not easily accepted)
Ideas:
1. Lamarckism
2. Blending= Any beneficial adaptation will be diluted & eventually disappear
Gregor Mendel
Inheritance
Founder of science of genetics
"Mendelian Inheritance"
Homologous trait or Analogous Trait?
1. Flight in birds and bats
2. Forelimb bone structure in whales, cats, and bats
3. Yellow and black coloring in poison dart frogs and wasps
4. The genetic code of Archaea and European starlings:
Analogous
Homologous
Analagous
Homologous
The height of parents and offspring were measured in three populations and graphed. If selection began to favor the shortest individuals, in which population would height evolve fastest?
C - Because HIGHEST INHERITANCE
Selection & genetic drift tend to ___________ genetic variation
= Reduce
Mutation, diploidy, neutrality, gene flow, & balancing selection can maintain genetic _____________ in a population.
= Variation
____________ are the ultimate source of genetic variability.
= Mutations
____________ & sexual reproduction result in novel genetic combinations
= Recombination
Recombination (definition)
The process or act of exchanges of genes between chromosomes, resulting in a different genetic combination and ultimately to the formation of unique gametes with chromosomes that are different from those in parents.
Polyploidy only occurs in plants (True/False).
It is possible for polyploidy to cause a speciation event in only two generations (True/False).
False.
True.
Which statement(s) about peppered moths in England is(are) true?
a. In response to increased pollution, the mutation rate increased, which created more black morph individuals.
b. Environmental change before and after the Industrial Revolution altered the fitness of individuals with the white and black phenotype.
c. Directional selection changed the distribution of color phenotypes in the peppered moth population.
= B & C
Which of the following statements is not always true of a population of sexually reproducing animals:
a. A group of individuals that can potentially mate.
b. A group of individuals that occur in the same geographic region.
c. A population does not exchange genetic material with other populations of the same species.
d. Hardy-Weinberg equilibrium predicts genotype frequencies within a non-evolving population.
= c. A population does not exchange genetic material with other populations of the same species.
Sickle-cell Anemia is caused by what type of mutation?
Mechanical isolation, gametic isolation (sperm doesn't lock to egg),
C. Post-zygotic isolation mechanism
Reduced hybrid viability (ex. salomander), reduced hybrid fertility (ex. mule), hybrid breakdown (ex.grass can reproduce but problems in environment)
Some of the earliest documentation loosely describing evolution by natural selection is seen:
a. during the Enlightenment
b. in the writings of Aristotle on Empedocles c. from 14th Century Chinese scholars
d. in the writings of Lamarck
e. in the writings of Darwin
b. in the writings of Aristotle on Empedocles
4. (4pts) Which of the following did Darwin NOT see during his voyage to the Galapagos?
A. Numerous non-endemic species with body types that seemed well-suited to the local environment.
(He saw ENDEMIC; living)
Is it more common for a point mutation to have a negative impact on fitness than a positive impact?
Yes
As environmental variation increases, the heritability of a trait will decrease. This statement is:
C. Possibly true. We first must know the effect of environmental variation on phenotype.
14. (6pts) For each of the following mechanisms of evolution, list the assumption(s) of HWE that it violates.
T / F Oxygen was initially released into the atmosphere primarily as a by-product of protist photosynthesis.
False - photosynthetic prokaryotic organisms that emitted O2 as a waste product. (Protist = Eukaryotic)
The largest mass extinction event in history occurred approximately
C. 250 million years ago
Permian–Triassic (P–Tr) extinction event.
The earlier phase was probably due to gradual environmental change, while the latter phase has been argued to be due to a catastrophic event.
Examining the phenotypes of a population of nargles, you find that they are exceptionally transparent. Nargles have a greater chance of survival than somewhat transparent or opaque nargles. This type of selection is cosidered to be:
E. directional
Which of Charles Darwin's influences established extinction as fact through his work with fossils?
B. Georges Cuvier
A fossil of a giant sloth is found in an area & resembles other extant organisms living in the same place. This is an example of:
B. the Law of Succession
Which of the following does NOT tend to promote speciation?