REVISION by ilicaifengba


									REVISION        FROM B2.5 (6th Form)


      Until the end of the eighteenth century it was believed that the earth was created in six
       days and to suggest otherwise was to incur the wrath of the church.
      Jean Baptiste LAMARCK (1774-1829) believed in the inheritance of acquired
       characteristics. Changes to an organism during its lifetime became fixed and were passed
       onto the next generation. This brought about gradual changes in a species. Not supported
       by evidence (except in special cases of some bacteria).
      Charles DARWIN and Alfred WALLACE (1858) both proposed a theory of evolution in
       which species gradually change over time. Darwin called this process NATURAL

     He reasoned in this way:

     1.    All organisms have a high reproductive rate, but the food supply and other resources
           in the environment are limited. This leads to a continual struggle for existence among

     2.    Among the offspring there is variation in all characteristics. Some will be better
           adapted to the environment than others.

     3.    Those organisms possessing favourable variations will be able to survive longer in a
           given environment, and so will have more chance to hand on these favourable
           characteristics to their offspring.

     4.    Over a period of time each successive generation will be better adapted to the
           environment - i.e. the "fittest" will survive.

     5.    Eventually new species will evolve from the old species.

     Darwin amplified his views in his famous book "The Origin of Species".

      Modern interpretation of Darwin's theory
         - Evolution can be described as a change in the gene pool of a population from
         generation to generation.

      Although individuals are selected for and against by natural selection, it is populations
       that actually evolve.

      The key to natural selection occurring at all is the variation that is present in any

      All organisms have adaptations which are features which enable them to survive. It is
       these adaptations which are selected for in nature and improve an organism's chances of
       passing on its genes to the next generation.

               The evolution of long-necked giraffes

On average, a pair of rabbits produces a litter of six offspring four times a year. Since the offspring
mature quickly, millions of rabbits could be produced within a few generations. Using the words
over-production, competition and variation in your answer, explain why the world is not over-
populated with rabbits.


     1.     Meiosis      - independent assortment
            (B3.3)       - crossing over
                         - sexual recombination
            New combinations of genes result.

     2.     Multiple Alleles - when more than two alleles are possible at a gene locus there is a
            possibility that an organism can be produced which is different from either parent.

     3.     Mutations (B3.3) - give new variations.

     4.     Polyploidy - having three or more times (3n or more) the haploid (monoploid)(n)
            number of chromosomes.
            (NB: Polyploidy will be covered in detail later in the notes.)

3.   NATURAL SELECTION acts on the variations.

     Individuals in a population that are best suited (fitted) to the environmental conditions
     survive and leave behind the most offspring. They have a selective advantage over other
     variations in their generation. Changes in the environment may favour new variations and
     over time this can result in an evolutionary change.

     Examples of natural selection in action include:
     1.    Industrial Melanism in peppered moth
     2.    Sickle Cell Anaemia and Malaria.
     3.    Antibiotic Resistance.
     4.    Resistance to Insecticides.
     5.    Heavy metal tolerance in grasses - soil in waste tips around mines where ores were
           once extracted, contain high concentrations of heavy metals. These include copper
           and lead. Although such concentrations are normally toxic to plants and animals,
           some varieties of grass species are able to tolerate and colonise these polluted

     Choose one of the above examples and use it to explain natural selection.


      Types of Natural Selection

     a) Stabilizing selection - selection against individuals that deviate from the mean. The
        result is that the mean stays the same but variation is reduced. eg. sickle cell anaemia.

     b) Directional selection - Individuals to the left or right (but not both) of the mean are
        selected as parents for the next generation, the result being a shift in the mean in the
        direction of the selection. It is associated with gradually changing conditions. eg.
        Industrial melanism in peppered moths - increase in the dark (melanin) form of the
        peppered moth due to the darkened bark of the trees during the industrial revolution as
        a result of soot deposits.

     c)     Disruptive Selection - selection in which two or more variants are at an advantage
            and intermediate types are selected against. The mean moves in two different
            directions and can be the start of the formation of two new species (speciation). eg.
            Suppose a certain population of birds shows much variation in bill length. Conditions
            change so that good feeding opportunities increase for those with short bills and
            long bills but those with intermediate sized bills experience a decline in the plants
            producing fruits suitable for them. The population would divide into two distinct types
            - short billed and long billed.

 Gene migration (immigration and emigration). New alleles are introduced when immigrants
  arrived from another population possessing a different gene pool.
 Mutation - new alleles appear and are reshuffled.
 Changes due to chance
       - Genetic Drift - random events change allele frequencies in a population. This is significant
       in very small populations which do not have a complete range of all the alleles typical of
       that species. eg. differences in blood groups in different populations.
       - Founder Effect - occurs when a small number of individuals leave a large population and
       colonise new territory, such as an island. The colonists only bring with them a small random
       sample of the total gene pool which may lack many of the alleles present in the original
       eg. * NZ hares originated from 6 animals introduced from Australia.
           * Hedgehogs introduced from Europe to NZ in 1870's only small random sample.

 Human manipulation
     - Artificial Selection
               - domestication of dog, sheep, cattle
     - Inbreeding
     - Outbreeding


          Comparative anatomy
          Fossil record
          Biogeography
          Vestigial organs
          Embryology
          Biochemical

VIDEOS:        # 216 Understanding of Evolution
               # 191 Galapagos - A Living Laboratory
               # 87 Evolution


SPECIATION is the formation of a new species. Evolution is the mechanism by which speciation is
brought about. It involves changes in genotype (and phenotype) of a population. The adaptations
of the new species enable the organism to better exploit its environment.

Species        A group of organisms that belong to the same gene pool and interbreed in nature to
               produce fertile offspring.

Selection Pressure - the strength of natural selection for or against a particular characteristic.

The Process of Speciation

Allopatric species
Two species which occupy separate geographical ranges - unable to breed because they are
separated by distance or geographical barriers.

Sympatric species
Two species which occupy a common or overlapping geographical range. They are separated by
biological barriers.

Allopatric speciation
Speciation involving geographical isolation (as above).

Sympatric speciation
Speciation, which can arise not involving a period of geographical isolation (see further notes).

ISOLATING MECHANISMS - prevent gene glow.

1.     Geographical Barriers - Shifts in continental plates (continental drift) eg. break-up of
       Pangea/Gondwana. (NZ split away from Gondwana 80 million years ago before mammals
       had evolved.)
       - mountain ranges - Southern Alps in NZ has divided the South Island into two very different
       climatic zones.
       - rivers
       - deserts
       - seas - islands. eg. NZ robins (see pg. 234 Designs of Life)

2.     Ecological Barriers - organisms have developed genetic differences to cope with different
       ecological niches or habitats. (i.e. different adaptations have been selected for as the
       environment has changed.)

3.     Climatic Changes - temperature changes resulting in changes in sea level (ice ages) or
       producing climatic "islands" or mountains. eg. During an ice age the sea level is lower -
       land masses joined. Read pgs 213 Study Guide and pg. 229 Designs of Life.

4.     Reproductive Barriers (Biological Barriers) - prevention of two species producing fertile
       offspring. These are two types:
       a)      Pre-zygotic isolation - these occur before fertilization.
                Habitat differences - may live in same area but occupy different habitats.
                  eg. Hocksetter's and Archey's frogs are both on the Coromandel but occupy
                  different habitats.
                Temporal (time including seasonal)
                   - timing of mating may be prevented by one being nocturnal, diurnal, active at
                     different times of the year, active on certain tides. Breeding seasons different.
                  eg. Silver pine sheds pollen in mid-late October, while rimu releases pollen in
                Structural - shape of genitalia means mating not possible. eg. insects may be
                  shaped in a specific way so as to not interbreed.
                  - co-evolution of flowering plants and pollinators.
                Gamete incompatibility - mating may occur but gametes do not fuse - chemicals
                  wrong; in plants pollen tubes do not develop.
                Behavioural - different courtship rituals including differences in vocalisations. eg.
                  native crickets, cicadas, grasshoppers as well as birds and frogs!
                  Production of nectar at different times of the day attracts different pollinators.

       b)     Post-zygotic isolation - prevents successful reproduction after fertilization.
              Hybrid inviability - zygote forms but dies (eg. mismatching of chromosomes)
              Hybrid sterility - hybrid forms but is infertile. eg. mule - no pairing of chromosomes
               during meiosis  gametes.
              Hybrid breakdown - hybrids (F1) are fertile but their offspring (F2) are sterile.


The following statements relate to the process which gives rise to allopatric species.
Read them carefully and write them in the correct order in the space below.

       1.    Mutations occur at random in each sub-population, giving rise to new variations
             within each group.
       2.    The members of a large population of a species occupy an environment. They
             share the same gene pool and interbreed freely.
       3.    Over a very, very long period of time, selection pressures acting on variations in
             each sub-population cause the gene pools to become so altered that the groups
             become genetically distinct and isolated.
       4.    The population becomes split into two completely isolated sub-populations by a
             geographic barrier which prevents interbreeding and gene exchange.
       5.    Reduced selection pressure resulting in a population explosion and expansion
             into new areas.
       6.    Interbreeding can no longer occur and two distinct species have evolved.
       7.    The selection pressures acting on each sub-population are different depending
             on local conditions. Natural selection affects each sub-group in a different way
             by favouring those alleles which make the members of that sub-population
             better at exploiting their environment.

Read pages 228 Designs of Life
           211 Study Guide (Hanson)
Activity:    p232 Designs of Life
Using information from pgs 215-217 (Hanson) write your own notes on how the Kaka and the Kea
arose as two separate species. (Set out as a series of stages.)

                              ASSIGNMENT 1                  (10 marks)

1.    Colonization of the Galapagos Islands by Finches

The following statements relate to the diagrams. Write out the statements in the correct order and,
beside each, put the letter of the diagram which corresponds to it.

a)   The finches increased in numbers and,
     under the influence of natural selection,
     gradually became adapted to the local
b)   Some finches from the second island
     managed to fly back to the first island,
     but reproductive isolation had occurred
     between them and the existing
c)   Originally, there were no finches on the
     islands. Some finches from the mainland
     managed to fly across to them.
d)   Some of the finches managed to fly to a
     second island where the environment
     was different.
e)   This process was repeated over and
     over again as the finches colonised
     more and more of the islands.
f)   Adaptation to the conditions on the
     second island gradually took place.


The diagram shows the distribution of two species of tree frog, Hyla ewingi and Hyla verreauxi, in
South East Australia. Oscillographs (sound traces) of the male mating calls are also shown.

a)   Describe what is meant by the terms allopatric species and sympatric species. (1)
b)   Explain the significance of a geographical barrier in the process of speciation.      (2)
c)   Explain the meaning of "natural selection".                                           (2)
d)   Discuss from an evolutionary point of view, why the mating calls of the two species of tree frog
     are similar in areas where only one of the two species is present, but markedly different in
     areas where both species live.                                                        (3)

One species gives rise to two or more species without prior geographic isolation. It is much rarer
than allopatric speciation and occurs mainly in plants.

 Instant speciation by Polyploidy.

Polyploidy - a new plant acquires an extra set of chromosomes due to the failure of chromosomes
to separate in cell division (non-disjunction - see notes in B3.3). Triploid - 3n or tetraploid - 4n
individuals can result which are genetically different to their parent plant and can be regarded as
new species.

       1. Allopolyploidy: - two different species contribute chromosomes
         eg. rice grass (Spartina townsendii) is an allotetraploid formed by

               Spartina maritima             x               Spartina alterniflora
                AA    2n = 56                                BB 2n = 70
                      (n = 28)                                   (n = 35)

                                     Sterile Hybrid
                                                               (chromosomes cannot form
                                      AB 2n = 63               homologous pairs during meiosis
                                                                no gametes formed )

                                 Can grow vegetatively
                                                         chromosome number doubles by
                                                         non-disjunction (amphiploidy) at

                                     Spartina townsendii

                                     AABB 2n = 126          fertile as homologous can pair at
                                                            meiosis to give gametes

       2. Autopolyploidy: - one species contributes the chromosomes

                      AA            x                 AA
                                                                 diploid gamete produced during
                                                                 non-disjunction at meiosis
                 A     A                             AA
                                    AAA         sterile hybrid - autotriploid unable to
                                        3n      form gametes (can grow vegetatively)

                       AA           x                AA
                                                                diploid gametes produced by
                                                                non-disjunction at meiosis
       gametes              AA                AA

                                    AAAA        fertile tetraploid
                                        4n      - homologous pairs of chromosomes
                                                give rise to viable gametes.

       Tetraploids (AAAA) can also arise by spindle failure during mitosis in a cell of AA. The
       polyploid cell divides normally to form a polyploid side shoot on the diploid plant.

Advantages of Polyploidy

Many commercial plants are polyploids and often show "hybrid vigour" - they grow faster, bigger,
are disease resistant and produce more offspring than their parent plant. eg. chrysanthemums,
Easter lilies.

Methods of inducing Polyploidy

Scientists can manipulate chromosome numbers by:
1. Using the chemical colchicine which prevents the spindle fibres forming during meiosis.
    eg. blueberries, cabbages.
2. Exposing plants to higher than usual temperatures, eg. maize.
3. Decapitation - a bud is removed and some new shoots developing from the scar tissue can be
    tetraploid. eg. "super tom" tomatoes.

                                       ASSIGNMENT 2

1. The diagram below illustrates the origin of bread wheat. Bread wheat, Triticum aestivum is the
   most widely cultivated plant in the world. It is a polyploid. Three diploid wild grasses were involved
   in its origin, each one contributing a different genome. The three genomes, ie. the three different
   sets of chromosomes, are represented as A, B, and D.

    Wild Einkorn wheat                               X                              A wild diploid Wheat
    Triticum aegilopiodes                                                                  (BB)
            (AA)                                                                         2n = 14
          2n = 14
                                               Sterile diploid
                                                  2n = 14

                                                         chromosome doubling (polyploidy)
                                      Wild Emmer wheat (tetraploid)
                                      Triticum dicoccoides (AABB)
                                                 2n = 28

         A wild diploid Wheat                       X            Cultivated Emmer Wheat (tetraploid)
         Triticum tauschii                                       Triticum dicoccum (AABB)
              (DD)                                                         2n = 28
             2n = 14
                                           Sterile triploid Wheat
                                                  2n = 21

                                                         chromosome doubling (polyploidy)
                                   Cultivated Bread Wheat (hexaploid)
                                            Triticum aestivum
                                                  2n = 42

    a)      Write a sentence to explain the meaning of the term polyploidy.                            [1]
    b)      Explain why the wild F1 hybrid (AB) is sterile.                                            [1]
    c)      What significance does polyploidy have for plant breeders?                                 [2]
    d)      What advantage does polyploidy confer on plants in the wild?                               [1]

2. A plant species A, which has 7 chromosomes in its gametes, was crossed with a related
   species B which has 9 chromosomes in its gametes. Hybrids were produced, but they were
   sterile. Microscopic observations of the pollen mother cells of the F1 showed no pairing by
   chromosomes. A section of the hybrid that grew vigorously was propagated vegetatively and
   a plant was produced with 32 chromosomes in its somatic cells. What steps might have been
   involved?                                                                                           [2]

 Ecological Speciation
      - can arise from a change in niche or lifestyle, where mating can only be between those who
      have adopted a new lifestyle. eg. a new host plant or new food.
 eg. Lice living on different parts of a bird host (eg. head, body feathers) have adapted to these
      different habitats and evolved into different species.


 Cline - gradient of variation in a population of a species due to having an extended geographical
      range. eg. Alpine buttercup, Ranunculus insignis - grows in mountains from South Canterbury
      to East Cape. Stem height, number of lobes on leaf margins show a north to south gradient.
      See pg 230-234 Designs of Life.

 Ring Species - A circular gene pool with interbreeding in a smooth graduation of characteristics.
      The series of individuals would be considered to be species except that the overlapping
      'ends' of the ring are reproductively isolated. eg. Herring Gull and Lesser Black Backed Gull
      have a chain of sub-species around the North Pole. Each sub-species can breed with those
      on either side of it, but the Herring Gull and Lesser Black Backed Gull cannot.

In both cline and ring species, gene flow is continuous between neighbouring sub-species so they
are considered to be one species. If the intermediate populations became extinct then separate
species would be established.

Natural selection is a complex process, operating continuously in all populations. It has the effect of
producing different patterns of evolution.
       - Divergent evolution including the process of adaptive radiation
       - Convergent evolution
       - Parallel evolution
       - Sequential evolution

Divergent Evolution
When an ancestral species evolves into two or more species that have become specialised to
occupy different ecological niches. When divergent evolution involves a large number of species
occupying different niches the process is called adaptive radiation. This is a relatively rapid
process. A group of related organisms which have undergone adaptive radiation are found to
possess homologous structures - those arising from one ancestral structure. eg. Pentadactyl limb.

Examples of Adaptive Radiation. (See Designs of Life pages 235-240)
      Darwins Finches, NZ Hebes, Molluscs, Ratites, Marsupials, Mammals


Placental Mammals

       Appeared 70 million years ago, within 10 million years the following forms had arisen.
                          Primates eg. Monkey
                                                                 Limbs - elongate, wide range of
                                                                 motion, toes long and flexible.
                                                                 Teeth - cheek teeth usually smooth
                                                                 surfaced and flattened for crushing.
                                                                 Other features - Tail sometimes
                                                                 prehensile: diet mostly fruit and

                           Chiroptera eg. Bats
                                                                 Limbs - Forelimbs and especially
                                                                 fingers of forelimbs elongate to
                                                                 support wing.
                                                                 Teeth - various for diets of insects,
                                                                 fruits and nectar, or other specific
                                                                 Other Features - Tongue, stomach
                                                                 and intestine various correlated
                                                                 with diet.

1st Placental mammal

                           Cetacea eg. Whales
                                                                 Limbs - shortened; feet enlarged
                                                                 and paddle shaped or absent.
                                                                 Teeth - Various but usually show
                                                                 herbivorous adaptation.
                                                                 Other features - Tail or hind limbs
                                                                 often modified into swimming

                           Perrisodactyla eg. Horse
                                                                 Limbs - elongate, toes elongate and
                                                                 reduced in number. eg. hoof of
                                                                 horse is one toe-nail.
                                                                 Teeth - incisors for nipping grass;
                                                                 cheek teeth heavy and ridged to
                                                                 withstand wear of grass.
                                                                 Other features - Horse intestine
                                                                 large and complex. Long caecum.

Convergent Evolution

Two or more species evolve from different ancestors so have similar features in response to similar
niche requirements. Structures that are used for the same purpose in unrelated species, but have
evolved from different origins are said to be analogous. They are superficial.
       eg. Wing of a bird and wing of a bee.
            Eyes of octopus and vertebrates. Octopus eye does not have an inverted retina.
            Many unrelated alpine plants have evolved a similar small-leaved, low-growing habit.
            Streamlined shape in dolphins and sharks and penguins.
            Divaricating shrubs in NZ.

Parallel Evolution

The evolution of similar anatomical or physiological features by related groups of organisms, eg.
South American and African porcupines evolved spines independently. Flightlessness has occurred
independently in a number of N.Z. chafer beetles (genus Prodontria) in the South Island.
NB:    There is really no clearcut distinction between parallel and convergent evolution - depends on
       the distance between the evolutionary starting points.

       Co-evolution: - many species have evolved relationships with other species in which
       they are totally dependant on each other. eg. mutalistic relationships - flowering plants
       and pollinators, NZ eg. Woodrose and Bat.

Sequential Evolution
When a species changes so much over time that it becomes sufficiently different to be classified as a
new species.

               Species A                       Species B

Species A no longer exists. It is reproductively isolated by time.

Gradualism vs Punctuated Equilibrium.

One view of speciation is that it usually occurs gradually by an accumulation of small (microevolutionary)
changes in gene pools over a long period of time.

Punctuated Equilibrium - in contrast, views species as changing most when they first diverge from
an ancestral species and then undergo relatively little change for the rest of their existence. Species
diverge in spurts of relatively rapid change, instead of slowly and gradually.
The two theories have stimulated ongoing debate among evolutionary researchers. Paleontologists
rarely find gradual transitions of fossil forms. Often species appear as new forms rather suddenly (in
geoglogical terms) in a layer of rocks, persisting for a long time unchanged and then disappearing as
suddenly as they appeared.

                             ASSIGNMENT 3 (20 marks)

1.   Distinguish between the following terms:

     (a)     allopatric and sympatric species
     (b)     autopolyploidy and allopolyploidy
     (c)     analogous and homologous structures
     (d)     prezygotic and post zygotic
     (e)     ring species and clines
     (f)     sterile and fertile hybrids
     (g)     convergent and divergent evolution
     (h)     directional and disruptive natural selection
     (i)     natural and artificial selection

2.   An octopus eye is very similar to a vertebrate eye. The former however, does not have an
     inverted retina and develops in a different manner. This indicates evolution from an ancestral
     line unrelated to the vertebrates.

     (a)     What does the term inverted retina mean?                                             [1]
     (b)     Are these eye types homologous or analogous? Explain your answer.                    [2]
     (c)     Have they arisen by convergent or divergent evolution?                               [1]

3.   The marsupial wolf of Australia is almost identical in body shape and life style to the placental
     wolf of the Northern Hemisphere. However, they are not regarded as being close relatives.
     Explain why.

                                                               Diploid             Hyploid
           Scientific name         Common name              chromosome          chromosome
                                                            number (2n)          number (n)
      Brassica derocea                cabbage                   18

      Brassica rapa                    turnip                                         10

      Brassica rapobrassica            swede                    38

     (a)     Complete the table.                                                                  (3)

     (b)     Scientists consider cabbage and turnip to be the original parents of swede but a cross
             between cabbage and turnip produces a sterile hybrid.

             (i)      State the diploid chromosome number of this hybrid.                         (1)
             (ii)     Discuss how the swede may have arisen from this hybrid.                     (3)

EVOLUTION AND SPECIATION TERMS    (Use the wordlist on pg 21 to complete)

                          Similar species living in different geographical areas.
                          Populations arranged in a circle across a species range are
                          unable to interbreed at the two ends.
                          A gradual phenotypic change across a geographical line.
                          Development of a new species involving a period of
                          geographical isolation.
                          All genetic information available to the members of a
                          Development of a new species whilst still in the same area
                          due to niche differentiation or polyploidy.
                          The change in allele frequency due to accumulated effects of
                          A process preventing interbreeding between members of
                          different populations.
                          Populations staying in constant form with sudden bursts of
                          change due to factors such as climatic change.
                          After the zygote has formed
                          Multiplication of the entire genome within a species.
                          Populations slowly diverge from one another by accumulated
                          adaptive characteristics through natural selection.
                          Before the zygote has formed.
                          Different groups converge on the same morphological lines
                          due to similar niche requirements. eg. streamlined body form
                          of shark and dolphin.
                          Similar species living in the same area.
                          The diversification of an ancestral group into two or more
                          Result of changes in gene pool from one generation to the
                          next. Non branching evolution.
                          The evolution of many species from a common ancestor due
                          to niche specialisation.
                          A feature with no clear function and not subject to natural
                          selection. eg. kiwi wing.
                          Structures with similar function but different phylogenetic
                          origin. eg. eye of octopus and man.
                          Formation of a hybrid with sets of chromosomes from two
                          different species.
                          Same structure but different function due to niche differences
                          eg. pentadactyl limb.
                          A group of organisms that belong to the same species and
                          occupy the same location.
                          The total of an individual's genetic material.
                          Last stage of allopolyploidy. Sterile hybrid becomes fertile
                          hybrid by doubling its unmatching chromosomes so they have
                          homologous partners.
                          Where population numbers decrease to a few individuals,
                          then increases again but with reduced genetic diversity.
                          A group of organisms that normally interbreed in nature and
                          produce viable offspring.
                          Abiotic or biotic factors that affect the survival/reproductive
                          success of an organism.

                           A relatively permanent change in allele frequency over time.
                           When a small group of individuals become isolated from the
                           main parent population and their gene pool is not
                           representative of the parent population.
                           Unequal reproductive success of certain phenotypes, and
                           hence genotypes.
                           Movement of genes from one population to another.
                           An inherited feature resulting from natural selection which
                           makes an organism better fitted to its environment.
                           Not having the normal number of diploid chromosomes.
                           A change in genetic composition of one species in response
                           to a genetic change in another.
                           Generally refers to polyploidy causing a new species to
                           appear without undergoing a long period of genetic isolation.

Ring species            Genetic drift                      Gene pool
Allopatric species      Punctuated equilibrium             Isolating mechanism
Autopolyploidy          Sympatric species                  Cline
Convergent evolution    Co-evolution                       Gradualism
Sequential evolution    Adaptive radiation                 Divergent evolution
Vestigial organs        Analogous structures               Evolution
Homologous structures   Population                         Allopolyploidy
Population bottleneck   Species                            Genome
Sympatric speciation    Post zygotic                       Selection pressures
Pre zygotic             Gene flow                          Natural selection
Amphiploidy             Adaptation                         Founder effect
Allopatric speciation   Instantaneous speciation           Aneuploidy


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