Full Name: ____________________
Lab day & time: _______________
Changing Populations: Fill in the Blanks
Use the words below to complete each paragraph. Each word may be used more than once or not at all.
black Peppered moths
converge
diverge
environmental disturbances
gene flow
genetic drift
genetic variation
individuals
light Peppered moths
mutation
mutations
natural selection
offspring
population
random events
red flowered plants
white flowered plants
Populations may change through two major genetic forces including Natural Selection
and Genetic Drift. There are two other forces that may change a population but these two
are less important and include: Mutations and Gene Flow. These two forces provide less
of a change in a population because Mutation is very rare and Gene Flow tends to
equalize gene frequencies between populations (which tends to slow down change).
Natural Selection occurs because organisms with favorable traits have a better chance at
survival, and the longer an organism lives, the more offspring it may produce, so that
more of the next generation will have the favorable trait than in the previous generation.
Natural Selection is when Individuals of one phenotype are favored over those of other
phenotypes. An example of this was when the British trees were covered in soot, the
black Peppered moths were favored over the light Peppered moths. When the British
cleaned up their air, the tree soot decreased, and the light Peppered moths increased in the
population.
Genetic Drift is a difference in reproduction or survival between organisms that is due to
random chance. Random chance events can happen in a population because various
Environmental disturbances can cause genetic drift, such as when Hurricanes or
Volcanic eruptions disturb a population. Human activity may also cause Genetic Drift
such as when humans clear the land for development or Over-hunt a population. Genetic
drift can also be from random events, such as when seeds from white flowers are blown
to gravel and some seeds from red flowers are blown to good soil. In the next generation,
there will be more red flowered plants because of genetic drift.
Mutation can create new genetic variation by changing DNA and thereby changing
genes. This does not happen very often though; it only happens around 1 in a million.
Gene flow, genetic drift and natural selection act on genetic variation in a population,
changing allele frequencies and thus changing the population.
Gene Flow tends to equalize allele frequencies between two populations, thus tending to
make the populations become more similar. Genetic drift and natural selection tend to
diverge allele frequencies between two populations (causing the populations to tend to
diverge)
Changing Populations: Define these terms
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Mutation -creates new genetic variation (or new genes)
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Shared inherited characteristics – characteristics that are shared between related
organisms because they were passed down from a common ancestor.
Adaptation –a characteristic that improves the survival of a population or
individual
better fit –an individual or phenotype that is more likely to survive and reproduce
in a given environment.
Species –organisms that are reproductively isolated from other organisms that are
not in their species, meaning that one can only reproduce within one’s own
species
Hybrid offspring –an offspring from two differing parents.
Speciation –when one or more species diverges into two or more species
Evolution –when an allele frequency is changing in a population
Changing Populations: Fill in the Blanks
Use the words below to complete each paragraph. Each word may be used more than once or not at all.
allele frequency
breeds of dogs
dark and light Peppered moths
Darwin’s speciation
day
evolution
evolving
individuals
macroevolution
microevolution
populations
time
Evolution is a change in the genetic characteristics of a population that happen over time.
This time period can be long or short. If any allele frequency in a population changes
with time, the population is evolving. Most people think of evolution as Darwin’s
speciation, but this is not correct. Only populations can evolve; individuals cannot
(though on the molecular level, genes can evolve). There are small scale changes that are
called Microevolution (such as seen in the change in the allele frequencies that caused a
change in the number of dark and light Peppered moths), and large scale changes that are
called macroevolution (such as can be seen in the different breeds of dogs).
Briefly Answer these Questions:
Why is natural selection the only force that works to better adapt organisms to their
environment? Natural selection is the only force that changes a population in the
direction of improvement. Mutation and genetic drift are not directional, they are
random. Gene flow tends to equalize gene frequencies regardless if it is against or with
the direction of improvement.
Why does adaptation never reach perfection? Environments change and new genetic
variation arises, so adaptation never reaches perfection. Adaptation must also use or
modify what is available, it cannot simply build what it needs. If there is no genetic
variation, there can be no adaptation. There may also be developmental or ecological
trade-offs. What is good at one time may be bad at another time, so that adaptation can
never reach perfection.