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Mechanisms of Evolution
Genetic ________ of individuals within a population makes evolution possible. ______ reproduction
creates a large amount of this _________ as individuals inherit a combination of _______ (traits).
In addition, __________ (permanent changes in DNA) happen randomly providing for the potential
of new traits to _________ on their own. Although variation in a population occurs randomly,
natural selection acts upon that variation in a non-random way.
Evolution can be divided into two main categories:
Macro-evolution is evolution on a ________, such as the evolution of a ___________ from
a common ancestor
Micro-evolution is the change in the __________________ (a shift in the ___________)
within a population over time - it is evolution ____________________
Factors that can lead to the shift in gene frequencies include:
Mutations - _________ changes in _____ that can affect the gene pool
Gene Flow –
The ________ of alleles from one population to
another due to ___________.
The addition of new alleles to a population will
__________ diversity and may help the
population survive.
Non-random Mating - Individuals in a population select mates often based on their ___________
features. Examples: caribou
antlers and peacock feathers
Genetic Drift -
Founder Effect -
Change in gene frequencies because
of ______________ events. Drift
has a greater effect on ________
a change in a gene pool that occurs
when a few individuals _______ a
new ___________ population.
Example: island colonization.
Bottleneck effect - a change in the gene pool caused by a ______________ in population.
Example: natural disaster.
Natural Selection - alleles that help an individual survive and reproduce will accumulate in the
population, leading to a shift in the gene frequencies.
Types of Selection
Selective Pressures can result in different patterns of natural selection. Characteristics can be
selected for (__________ selection) or against (_________ selection).
Directional Selection – occurs when selection favours
individuals with a more ___________ variation of a trait.
The result is a shift away from the average condition.
Example: strawberries are selected for larger and
sweeter fruits, thoroughbred horses for running speed.
Stabilizing Selection – occurs when the __________
characteristic within a population is favoured by the
environment. Example: human birth weights are subject
to stabilizing selection.
Disruptive Selection – favours individuals at _________________________ of a characteristic.
Example: male coho salmon – small 500 g or large 4500 g.
Sexual Selection – the favouring of any trait that specifically enhances the _____________ of an
individual. Sexual selection often leads to the males and females of a species evolving appearances
and behaviours that are quite _______ from each other (________________). Example: males
often evolved larger body size and other attributes (antlers) that are used in direct ___________
for mates. Some of the features selected for by sexual selection, can become a ___________ for
the __________ of the individual. Example: large or brilliant coloured plumage make for easy prey.
Patterns of Evolution
Adaptive Radiation – occurs when a single species evolves into a number of distinct but _________
__________ species (Galapagos finches), usually occurs when a variety of new resources not being
used by other species becomes available.
Divergent Evolution - one or more new species are produced by changes to the initial organism
("___________"), each branch gives rise to a new species and "parent" can still exist.
Example: Northern Ontario rodents – beaver, flying squirrel, porcupine
Convergent Evolution – occurs when two different species evolve to
occupy similar ecological _________. Example: streamlined body
shape of the dolphin and shark
Coevolution – a process in one species evolves in ___________ to the
evolution of another species. Example: the Madagascar long-spurred
orchid and the hawk moth