This document provides information on various concepts related to evolution and speciation. It defines key terms, describes mechanisms of natural selection and speciation, and outlines different patterns of evolution such as divergence and convergence. Examples of evidence for evolution are also mentioned, including fossils, comparative anatomy, embryology, biogeography, and molecular biology studies.

1. Speciation
300 BIOLOGY
GB
2014

2. Achievement Standard
Evolutionary processes involve the following biological ideas:
 Role of mutation
 Gene flow
 Role of natural selection and genetic drift
 Modes of speciation (sympatric, allopatric)
 Reproductive isolating mechanisms that contribute to speciation (geographical, temporal,
ecological, behavioral, structural barriers, polyploidy)
 Patterns such as divergence, convergence, adaptive radiation, co-evolution, punctuated
equilibrium, and gradualism.
Scientific evidence for evolution, which may include examples from New Zealand’s flora and
fauna, will be selected from:
 fossil evidence
 Comparative anatomy (homologous and analogous structures)
 Molecular biology (proteins and DNA analysis)
 Biogeography.

3. The Basics
Terms:
 Genes – carry the genetic information required for cell growth, functioning and replication
 Alleles – alternative form of a gene (creates variation)
 Gene Pool – all the alleles of a population
 Gene Flow – movement of alleles in and out of a population
 Speciation - evolution of new species, new species cannot reproduce with old species
 Mutation – change in the base sequence in DNA, must occur in gametes to be passed on.
Creates totally NEW phenotypes.
 Bottleneck Effect – massive loss of alleles due to natural disaster, leaves a non
representative population
 Founder Effect – small non representative group migrate to a new habitat
 Genetic Drift – random loss of alleles due to chance in a small population

4. Natural Selection
Natural Selection – those best suited to their
environment mate and pass on their genes to the
next generation increasing the number of these
helpful genes in the gene pool, meanwhile those
unsuited do not mate and those genes disappear
from the gene pool.
 Stabilizing selects against the two extremes and
favors the middle (2)
 Directional selects against one of the extremes (3)
 Disruptive selects against the middle and favors the
two extremes, this can lead to speciation (1)

5. Variation
 Differences between individuals in a species, caused by
differences in the DNA base sequence
 The more differences in a species the greater chance that
some of the species will survive changes within their
environment
 Variation is created during sexual reproduction, meiosis (crossing
over, independent assortment, segregation) immigration and
mutations
 Variation must occur within the gametes in order to be passed
on
 Variation is reduced by natural selection, genetic drift
(bottleneck effect, founder effect), emigration and natality.

6. Speciation
 One species evolves into two or more species that can no
longer interbred.
 Usually occurs as a result of adaptation to new ecological
niches and in response to the occurrence of new variations
within the species that make an organism better able to survive
and reproduce

7. Speciation
There are three ways in which new species
can evolve:
1. Instant Speciation
 Occurs within one generation as a result of
polyploidy
 more than two sets of chromosomes
 Usually occurs in plants

8. Speciation
2. Sympatric Speciation
 Occurs when a new species arises in the SAME
territory as the parent species
 Often occurs as a result of niche differentiation
(ie finches living in top of trees vs forest floor)
3. Allopatric Speciation
 Occurs when a new species evolves as a result
of being isolated from the parent species
 NEW territory
 Often occurs when there is some kind of
geographical or environmental disturbance

9. Polyploidy and Aneuploidy
 Poly – many, polyploidy = more than one set of chromosomes
 Aneu – one, aneuploidy = one chromosome is represented
three times instead of the usual two (one from each parent)
 Homologous Chromosomes usually separate during meiosis to
create two gametes with haploid (n, half the original)
chromosomes
 Non disjunction – when homologous pairs of chromosomes fail
to separate during meiosis the gametes can end up with:
 Having two copies of a single chromosome (aneuploidy)
 Having a missing chromosome (aneuploidy)
 Having 2 whole sets of chromosomes (polyploidy)
 Having NO chromosomes (zygote is unlikely to form in this case)

10.  Offspring formed from these gametes end up having:
 3 or more of an individual chromosome – aneuploidy
 3 or more sets of chromosomes – polyploidy
 Polyploidy generally only occurs in plants and can be advantageous as often
results in bigger better crops, or seedless crops (infertile plants have no seeds!)

11. Aneuploidy in the sex chromosome in
humans can result in:
Turners Syndrome – XO
 Klinfelters Syndrome – XXY
Aneuploidy in an autosomal
chromosome in humans can result in:
Downs Syndrome – trisomy 21 – 3 number
21 chromosome
Edwards Syndrome – trisomy 18 – 3
number 18 chromosomes

12. Types of Polyploidy
 Polyploidy can result in both sterile and fertile offspring
 In order to be fertile an organism needs to have an EVEN number of chromosomes (so they
can line up in homologous pairs and separate during meiosis
 Autopolyploids – organisms with multiple sets of chromosomes from the SAME species
 Eg a potato produces gametes with polyploidy (more than one set of chromosomes) and mates
with another potato giving rise to a new potato with autopolyploidy (3 sets of chromosomes but all
from the potato family)
 Often occurs when plants self fertilize
 If both gametes have undergone non disjunction then the offspring will be fertile as it will be have
an even number of chromosomes -4n or tetraploid
 If only one gamete has undergone non disjunction it will result in infertile offspring as there will be
an uneven number of chromosomes – 3n or triploid

13.  Allopolyploids – organisms with multiple sets of chromosomes from DIFFERENT species
 Eg a wheat plant fertilizes a rye plant
 If the offspring has an uneven number of chromosomes due to non disjunction having occurred in one of
the gametes then the offspring will be infertile
 If the offspring has an even number of chromosomes due to non disjunction occurring in both gametes
then the offspring will be fertile
 If the uneven numbered gamete manages to fuse with another normal gamete and a plant with even
chromosomes arises then it will be a fertile hybrid – this usual occurs as a result of self fertilisation.
 Hybrid – made from two different species

15. Isolating Mechanisms
 In order for a new species to arise it must not be able to reproduce with
the parent species.
 Prevention of reproduction can occur in several ways:
1. Pre Zygotic (before a zygote is formed)
 Geographical – separated by space, river, ocean, mountain, road etc
 Temporal –reproducing at different times of year, active at different times of day
 Ecological – live in different ecological niches
 Behavioural – different courtship behaviours
 Structural barriers – reproductive genitalia incompatible
 Gamete incompatibility – pollen grains don’t grow pollen tubes

16. 2. Post Zygotic (once zygote has formed)
 Polyploidy – multiple sets of chromosomes, in an uneven number so that
offspring are infertile
 Hybrid Inviability – zygote is aborted as has chromosomal
incompatibility
 Hybrid Sterility – off spring survives but is sterile – mule
 Hybrid breakdown – hybrid is fertile but its offspring are sterile

17. Evolution
 Evolution - the gradual change in species over long periods
of time resulting in establishment of a new species, (lots of
speciation's occurring one after the other over millions of
years!)
 Variation of alleles exists within the population
 The organisms are exposed to a selective pressure such as
a changing environment
 Those with favorable phenotypes are more likely to survive
and reproduce while those with less favorable phenotypes
have less chance of surviving and reproducing. “survival of
the fittest”
 Each generation will be better adapted to the current
environment.

18. Patterns of Evolution
Speciation or evolution can occur in a variety of ways:
 Divergence (A)
 Common ancestor, but no longer look the same
 Humans and apes from a common primate ancestor
 Convergence (B)
 Unrelated ancestor, but look similar due to similar selction pressures due to living in similar environment
 Whales and fish look the same as both live in water but NOT related
 Parallel Evolution (C)
 Unrelated ancestor, dissimilar environment but still look similar
 Adaptive radiation
 Co-evolution
 Species which are unrelated but have a close ecological relationship exert selection pressures on each other
 Predator /prey eg flowers grow to allow certain birds to pollinate, birds develop long beaks so can get pollen

19. Rate of Evolutionary Change
 Gradualism
 Slow progressive change over time
 Punctuated equilibrium
 Generally slow change but with periods of rapid
evolution
 Caused by rapid and extreme changes to the
environment
 Eg ice age, volcanic eruption

20. Evidence for Evolution
 Fossils – comparison to current day species
 Comparative Anatomy
 Homologous structures
 Same origins but different function
 Forelimb bones of birds, humans, whales, bats
 Analogous structures
 Different origins but similar functions
Wings of bats, birds, and moths

21.  Embryology
 The more similar embryos are of different species the less time has past
since they diverged
 Bio geographical – geographical origins of current species
distributions
 Biochemical – similarities between DNA and proteins

22. The End