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2009 SUMMARY EVOLUTION 1
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For tutorial & any assignments passed up:
 Since we are starting to prepare for “A-levels”
 Each point must be in separated paragraph
 Otherwise assignment will not be marked
 Yippy

2009 SUMMARY EVOLUTION 1
Linnaeus Binomial system of classification
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Definition of species
1 What is variation; why is variation important
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= raw material for natural selection
2 Darwin’s theory of evolution
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7 Steps in argument
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Neo-Darwinisn
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2 examples: Industrial melanism; ; finches
3 How does natural selection bring about evolution = SPECIATION?
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Directional / disruptive / stabalising
4 Speciation
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Allopatric / sympatric
5 Source of variation
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Mutation: DNA/chromosomal
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Meiosis: X-ing over / independent assortment / random fusion gametes
6 What changes allele frequency in a gene pool?
1 Mutation
2 Natural selection
3 Gene flow
4 Genetic drift: random / Founder principle / Bottle neck effect
5 Non-random mating
7 Why is the population the smallest unit that can evolve?
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Population = group of interbreeding individuals
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2009 SUMMARY EVOLUTION 1
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1 Explain the binomial nomenclature of a species and hierarchical classification.
A.
the binomial nomenclature
1 Each species has 2 part name: genus species
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genus caps; species lower case
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in italics; names are Latinized
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UNDERLINE
2 Purpose: Use of universal common scientific name to avoid ambiguity
B. Explain hierarchy of classification. (Linnaeus)
1 Groups organism mainly on similarity of morphology.
2 Define taxon = Basic unit of classification. A taxon is a group of organisms occupying
a particular level in a classification system.
3 In the Linnaeus system there are 7 taxonomic groups: Kingdom; phylum; class; order;
family; genus; species. (King Philip Came Over For Good Soup)
4 Kingdom is the largest and most inclusive group; species = smallest category
5 (LATER ~ Organisms grouped on assumed homologies. The more homologies two
organisms share the closer they are in evolutionary distance.)
C. Definition of species
1 Biological: A group of organism that interbreed & producing fertile offspring
2 Phylogenetic definition: A group of organisms sharing unique set of features which
may include structural, morphological, chromosomal, molecular sequences.
3 (Ecological: A group of organisms occupying same niche in a geographical region.)
4 Genetics: group of organism sharing a similar karyotype.
2 Explain why variation is important in selection.
What is variation?
1 Phenotype differences in members of a population that are inheritable or can be
passed on to subsequent generations
2 These include morphological, physiological; behavioral traits
Importance of variation
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1 Is the raw material for natural selection.
2 Variation allows some individuals in a population to survive better, increasing their
chance of maturing, producing, passing their favorable characteristics to their
offspring.
3 Allows adaptability of a population to changing environment, ensuring a species
survives changes
Explain Darwin’s theory of evolution
Intro
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Darwin proposed that evolution occurs through natural selection:
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Natural selection refers to the differential success in reproduction of different
individuals in a population resulting from the interaction of organisms with their
environment.
Steps in argument
1 populations have capacity to increase exponentially
2 populations remain same size
3 There is competition for limited resources (food; mates; habitat; etc)
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Other environmental factors may also affect survival: ability to overcome
predation, disease etc
4 There are variations in individuals in a population (morphological, physiological,
behavioral etc); these traits are inheritable
5 Variation within a population provides the raw material for natural selection.
6 Individual with favourable traits (to the particular environment) are more likely
survive to adult and pass on traits to offspring; vice versa.
7 Over time proportion of individual having favourable traits accumulate in population
8 Over (many)n generations there may be sufficient change in the population to form a
new species.
Explain neo-Darwinism
1 Explanation of evolution which includes knowledge on genetics (esp) and molecular
biology
2 Mutation = source of variation
3 Natural selection leads to change in allele frequency in population
4 Gene pool sufficiently changed a new species evolve
2009 SUMMARY EVOLUTION 1
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3 With ref to examples show how environment act as forces of natural selection.
A. e.g. Industrial melanism / Peppered moth
1 (Before 1948); peppered moths Bison betularia were light speckled coloured. They
camouflaged well on lichen covered trees.
2 Melanic forms exist from spontaneous mutation. melanic forms selected against in
non-polluted areas/pre-industrial time
3 In industrialized areas  soot from coal burning killed lichen leaving brown bark /
blackened tree trunks
4 Melanic forms became better camouflaged & selected for/survived; peppered forms
selected against
5 Moths were predated on by birds.
6 Melanic  increase in proportion with subsequent generations
7 In non-industrialized habitats light coloured moths predominated.
8 Clean up of pollution in industrial areas also saw a return of the peppered population
B. e.g. Darwin’s finches
1 Presumably, the ancestor of Darwin’s finches strayed from the South American
mainland of Ecuador to Galápagos Islands
2 Due to lack of competition/isolation from any main land bird species ancestral
finches spread to adapt to the different food niches available
3 The 13 species that evolved fall into 4 groups according to feeding habits:
4 Ground and cactus (seed-eaters), tree (insect-eaters), vegetarian (bud-eaters) and
warbler (insect-eaters) finches.
5 Food source was the agent of natural selection
6 Each group was subjected to a different set of selective pressures.
7 Although the islands are close to each other, environmental conditions were
different.
8 These circumstances & aided by the geographic isolation of the many islands,
Ancestral finches evolved into separate species.
Source of variation
1. Mutation
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2009 SUMMARY EVOLUTION 1
Change in structure or amount of DNA
i. Gene mutation: by Deletion; substitution; insertion; inversion
ii. Chromosomal level
a. Deletion; substitution; insertion; inversion
b. Change in chromosomal number
1. aneuploidy – 1 extra /less; e.g downs syndrome (+ chr. 21)
2. polyploidy – multiple sets chromosomes
2. Meiosis
i. Reshuffling of alleles
a. Crossing over – non sister chromatids  give new combination
alleles
b. Independent assortment  give new combinations of chromosomes
c. Random fusion of genetically diff. gametes
3. How does natural selection bring about evolution?
(Macroevolution) = changes in a population that involve formation of new species or
extinction of species
(Microevolution) = change in gene frequency in gene pool of a population that have
not yet generated a new species. May lead to adaptive changes
What are factors that may leads to change in allele frequency gene pool? (eventually
leading to speciation)
1 Mutation
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Defn. random change in DNA of organism  source of new alleles
2 Natural selection
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Differential success in survival and reproduction of individuals in a population
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Favourable phenotypes  higher chance of surviving to maturity and passing
favourable traits to next generation
3 Gene flow
(1) Migration / emigration of individuals brings new alleles into a population
4 Genetic drift
(1) Change in allele frequency due to chance
(2) Greater impact on smaller populations
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2009 SUMMARY EVOLUTION 1
(a) FOUNDER PRINCIPLE
1. a few individuals of old population colonise new habitat
2. Frequency of alleles of this sub-group is not representative of old
pop.
3. Subsequent generations produce a gene pool diff. from original
pop.
4. E.g. Amish community ; Darwin’s finches
(b) BOTTLE NECK EFFECT
1. Pop. Is drastically reduced in size by disaster/unfavourable
environmental change – epidemic; quake; fire
2. Allele frequency of surviving pop. Is not representative of original
pop.
3. Subsequent generations produce a gene pool diff. from original
pop.
a. E.g. N American seals hunted  20 survived and produced the
new generation
2 Non random mating
(1) E.g. Birds and mammals tend to prefer mates with a high degree of
symmetry
(2) Humans tend to prefer to mate with individuals of the same height and
colour.
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4. How does natural selection bring about evolution = SPECIATION?

produces a change frequency of heritable traits in gene pool
1. Directional selection
i.
Phenotype of one extreme selected for. What is initially rar is favoured
ii. E.g. Melanic form of the peppered moth has selective advantage in polluted
areas. Dark colour is due to a dominant melanic allele, whose frequency
increases in the population.
2. : Disruptive / Diversifying selection
i.
Intermediate phenotype selected against. Individuals at both extremes
selected for.
ii. Snails with pale shells are selected for in dry grasslands whereas those with
dark broad bands are favoured in areas with leaf litter.
3. : Stabilising selection
i.
Intermediate variants selected for. Extreme phenotypes selected against.
ii. Babies who are heavier or lighter than optimum birth weight are at a
selective disadvantage. Slightly increased mortality works against extremes of
birth weight in humans.
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4. Allopatric speciation = emergence of a new species when geographically separated
from its ancestral population
1. A small group of individual of a population move to a new habitat.
2. the two populations become geographically isolated and don’t mix
3. there is no mixing of their gene pools
4. each population evolves/adapts according to their different habitats
5. mutation may further change each gene pools
6. Eventually their gene pool becomes so different that 2 populations are no longer
able to inter breed. New species evolves
5. Sympatric speciation
= emergence of a new species while in the same geographically location as its
ancestral population.
Due to mutation, switch of habitat, food, mating preference, ecological niche.
Prezygotic
1. occupy same location but different habitat
2. Temporal isolation. Reproduce at different seasons
3. Behavioural isolation. Different courtship behaviour.
4. Unable to mate. Non-compatible genitalia
5. Gamete isolation. Pollen not compatible to stigma, do not germinate
Postzygotic
6. Low hybrid fertility
5. Why the population is the smallest unit that can evolve?
(Why not individuals)
1. Defn population: group of interbreeding individuals of a species in a particular
geographical location
2. it is members natural selection selects between individual of a population
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3. need a population of members before we can have variations on which natural
selection can take place
4. a population of members is needed to interbreed and pass on their genes to the next
generation
5. evolution is measured as changes in proportion of inheritable variations in a
population in successive generations
6. There is no variation to act on for a single individual.