Transcript File

 Biological
Species: populations where
individuals are able to interbreed to produce
viable offspring.
 Speciation
occurs when there is a dramatic
change and the population of species are no
longer able to interbreed.
 Thus
resulting in the formation of a new
species.
 Two
populations of species that are
reproductively isolated have little to no
gene flow in between them.
 There
are two main types of mechanisms
that reproductively isolate two groups of
species.
1) Pre-zygotic
2) Post-zygotic
 When
species are not able to mate or when
eggs cannot be fertilized.
 There
are a total of 5 different forms of prezygotic isolating mechanisms
 When
species have a specific signal or
behaviour it prevents closely related species
from interbreeding.
Both birds are very
similar in appearance.
Due to the differences
in their song, these
birds do not
interbreed.
Western Meadowhalk
Eastern Meadowhalk
 When
two species live in the same area but
have different habitats, they rarely interact
with one another.
Garter snake
(thamnophis sirtalis)
prefers open areas.
Garter snake
(thamnophis ordinoides)
commonly found near
water.
 Temporal
conditions refers to time of
day, year and seasons.
 Some
organisms mate at different
times which limits their interaction.
 This
is very common in flower
species.

Some species that are closely related
do not have compatible genital
anatomy.

This incompatibility prevents them
from mating.

This is very common in insects, for it
behaves as a lock-and-key system.

Plants also have different structures
that prevent the pollen from
fertilizing the flower.
 This
occurs when a species’ gametes are not
able to meet.
 The
gametes are not able to survive within
the female’s reproductive tract which
prevents the gametes from interacting.
 There
are times when the sperm and egg
meet, however the zygote cannot develop
into a viable offpsring.
 As
a result, species still remain distinct from
one another because their genetic
information does not combine.
 There
are 3 different post-zygotic
mechanisms.
 When
the genetic information is not
compatible between species.
 This
prevents the zygote from undergoing
mitotic division, and the zygote cannot
develop further.
 When
two species can mate and produce
viable offspring.
 The
hybrid offspring cannot undergo regular
meiosis and cannot produce eggs or sperm.
 The
hybrid offspring is thus sterile and
cannot propagate its genes into the
population.
 Two
organisms are able to mate and produce
viable and fertile offspring.
 When
the hybrid species mate, their
offspring are weak and sterile.
 This
limits the amount of generations in
which genes can propagate within the
population.
 In
order for speciation to occur, populations
of organisms need to be genetically isolated
from one another.
 Speciation
can happen in two main ways
depending on the gene flow between the
populations.
1) Sympatric Speciation
2) Allopatric Speciation
 Occurs
when the gene flow is interrupted
due to the divison of the population into
subpopulations.
 Separation
can occur due to river, water
level change, geological remodeling etc.
 The
separated gene pools evolve due to
different selective pressures in their
environment.
Because the population is
small, allopatric
speciation is more likely
to occur over a shorter
period of time.
 Occurs
when populations live in the same
geographical area and become
reproductively isolated.
 Because
these species live in the same
geographical area, there needs to be a
change in their genetic information.
 Most
of sympatric speciation is due to
chromosomal changes and non-random
mating.
Example 1: Polyploidy
 Causes
 Error
a reproductive barrier
in cell division resulting in an extra set
of chromosomes.
 During
meiosis, if the cells fail to separate
properly, cells become diploid instead of
haploid.
 Their
ability to self-fertilize enables these
diploid cells to fuse with one another to
produce tetraploid species.
 These
polyploid cells cannot be crossed with
a haploid or else it would form triploid cells
which are infertile.
 When
two species interbreed they produce a
sterile offspring.
 However,
the sterile offspring is able to
reproduce asexually, thus creating a new
population of species.
 Eventually
this polyploid population grows
because of self-fertilisation.
Divergent Evolution:
 Species that were similar to the
ancestral species diverge and become
increasingly distinct.
Convergent Evolution:
Similar traits arise because different
species have independently adapted
to similar envrionmental conditions.
 Gradualism:
views evolution as a slow and
steady pace before divergence.
 Big
changes occur due to an accumulation of
small changes.
 This
pattern of evolution is very rare within
the fossil record.
 Views
evolution as long periods of stasis
where no change occurs, which are later
interrupted by periods of divergence.
 Species
usually undergo a dramatic change
when they are first isolated and then
stabilize.
 This
is the most common pattern shown in
the fossil history.

Allopatric speciation may occur
when humans perform the
following activities
Convert
large stretches of
wilderness into croplands
Develop wilderness areas
for recreation or tourism


Build roads

Build urban subdivisions
 The
following human activities cause a
bottleneck effect within the population.

Unregulated hunting

Habitat removal