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Microevolution
Changing Allelic Frequencies
Adaptation is a beneficial gene that will help an
organism to survive and reproduce.
NOTE1. Evolution only works on phenotype not genotype.
2. Evolution works on populations not individuals.
Microevolution-how allelic frequencies in a population
change.
Macroevolution-how accumulations of changes, results
in new species or speciation.
This saddle-back tortoise
has an adaptation of an
elevated shell to reach
food others can not.
Adaptation is a beneficial gene that will help an organism
to survive and reproduce. They come from mutations.
NOTE1. Evolution only works on phenotype not genotype.
2. Evolution works on populations not individuals.
Microevolution-how allelic frequencies in a population
change.
Macroevolution-how accumulations of changes, results in
new species or speciation.
This saddle-back tortoise
has an adaptation of an
elevated shell to reach
food others can not.
Species-a group of interbreeding organisms that
produce viable and fertile offspring in nature.
Gene pool-sum total of all the genes in a given species.
Allelic frequency- is the percent occurance for a given
allele.
How does variation in a population arise?
1. Mutations and new genes provide the raw material
for evolution.
2. Meiosis and sexual reproduction will produce new
recombinants of phenotypes which natural selection
operates.
Species-a group of interbreed-ing organisms that
produce viable and fertile offspring in nature.
Gene pool-sum total of all the genes in a given
species.
Allelic frequency- is the percent occurance for a
given allele.
How does variation in a population arise?
1. Mutations and new genes provide the raw
material for evolution.
2. Meiosis and sexual reproduction will produce
new recombinants of phenotypes which natural
selection operates.
This wisteria on the right has a mutation
which causes white flowers instead of purple
Mutations and new genes
*MOST mutations are deleterious and recessive.
Gene level
1. point mutations
2. frame shift mutation
Chromosomal level
3. chromosomal rearrangement
a. inversion
b. deletion
c. duplicaton d. translocation
4. gene replication and modification.
EVOLUTION EDITS AND DOES NOT START
FROM SCRATCH.
Mutations and new genes
*MOST mutations are deleterious and
recessive.
Gene level
1. point mutations
2. frame shift mutation
Chromosomal level
3. chromosomal rearrangement
a. inversion b. deletion
c. duplicaton
d. translocation
4. gene replication and modification
EVOLUTION EDITS AND DOES NOT START
FROM SCRATCH
Some mutation do not change the functioning
of the protein. Therefore an accumulation of
mutations can be used as an evolutionary
clock. On the average cytochrome C mutates
every 17 million years. Between mammals and
reptiles there are 15 different amino acids or
mutations. That means that mammals and
reptiles diverged 265 million years ago. that
means that there was one mutation every 17
million years on the average.
Some mutation do not change the
functioning of the protein. Therefore an
accumulation of mutations can be used
an evolutionary clock. On the average
cytochrome C mutates every 17 million
years. Between mammals and reptiles
there are 15 different amino acids or
mutations. That means that mammals
and reptiles diverged 265 million years
ago. that means that there was one
mutation every 17 million years on the
average.
Myoglobin is a protein that binds with
oxygen in the muscles. This gene has
been through duplication and modified
many times. It has given rise to the
hemoglobin gene
Myoglobin is a protein that binds
with oxygen in the muscles. This
gene has been duplication and
modified many times. It has given
rise to the hemoglobin gene
If the following conditions are met then allelic
frequency remain the same and NO EVOLUTION
occurs.
Hardy-Weinberg Equillibrium
*1. Population must be large enough that chance is
not a factor.
*2. Population must be isolated (no immigration
or emigration) to prevent gene flow.
3. No mutations or mutational equillibrium
4. Complete random mating with respect to time
and space
5. Every offspring has an equal chance of survival
without reguard to phenotypes.
If the following conditions are met then allelic
frequency remain the same and NO EVOLUTION
occurs.
Hardy-Weinberg Equillibrium
*1. Population must be large enough that
chance is not a factor.
*2. Population must be isolated (no immigration
or emigration) to prevent gene flow.
3. No mutations or mutational equillibrium
4. Complete random mating with respect to time
and space
5. Every offspring has an equal chance of
survival without reguard to phenotypes.
1. Condition #1 can be met. It is important to have
large populations in order so that the loss of genes
will not be a factor. Small population can experience
genetic drift.
Also if a small population moves to another area,
chances are the gene pool will be different from the
original gene pool. This is called the founder effect.
2. Condition #2 can be met if the population is
isolated. If individuals come and go into a
population, the allelic frequencies change and
evolution occurs.
1. Condition #1 can be met. It is important to have
large populations in order so that the loss of
genes will not be a factor. Small population can
experience genetic drift.
Also if a small population moves to another area,
chances the gene pool will be different from the
original gene pool. This is called the founder
effect.
2. Condition #2 can be met if the population is
isolated. If individuals come and go into a
population, the allelic frequencies change and
evolution occurs.
3. Condition #3 can NEVER be met because one
can never stop mutations. Mutational equillibrium
can never be met.
4. Condition #4 can NEVER be met. Mating is
never random.
A piece of pollen from an apple tree in Ohio is more
like to pollinate a tree in Ohio than one in
Washington state.
5. Condition #5 can never be met. There will
always be variation. Some variation will help
organisms to breed and survive.
3. Condition #3 can NEVER be met because
one can never stop mutations. Mutational
equillibrium can never be met.
4. Condition #4 can NEVER be met. Mating
is never random.
A piece of pollen from an apple tree in Ohio
is more like to pollinate a tree in Ohio than
one in Washington state.
5. Condition #5 can never be met. There
will always be variation. Some variation
will help organisms to breed and survive.
Unstable variation-means that one trait is more beneficial
in a given environment than another and there is a
selection pressure operating on it.
Unstable variation-means that one trait is more
beneficial in a given environment than another and
there is a selection pressure operating on it.
Types of selection
1. Directional selection-in a given population there is
variation, one extreme is now favored over the other
phenotypes. This gives rise to an increase in the favored
gene. The allelic frequency changes and moves to the more
favored trait. Note-many traits are are controlled by many
genes (multifactorial inheritance). It is the combination of
the gene that allows for many phenotypes. Ex- Height is
multifactorial inherited.
i.e. The okapi and giraffe are thought to
have a common ancestor. There was a
selection pressure for the giraffe to have a
longer neck to obtain food that other
animals can not reach. Over time, that trait
was selected for.
Ex- This graph shows how researchers at U.
Illinois selected for an increase in the oil
content of corn through 50 generations
(directional selection). It is thought that this is
a polygentic trait (multifactorial) and that the
increase in oil resulted from new
recombinations of genes (more genes for oil
were "turned on" than new mutations
Types of selection
1. Directional selection-one extreme is favored over the
other phenotypes. This gives rise to an increase in the
favored gene. The allelic frequency changes and moves
to the more favored trait. Note-many traits are are
controlled by many genes (multifactorial inheritance). It
is the combination of the gene that allows for many
phenotypes. Ex- Height is multi-factorial inherited.
2. Disruptive selection (diversifying selection)-There is a selection
pressure for the two extremes, this causes an increase for the
traits at the extreme.
Ex- Suppose that gametes (sperm and eggs) were the same size
(isogamy). It is thought that there were two selection pressures
operating on the two types of gametes.
1. Selection pressure of storing food for future embryo would
work on eggs.
2. Selection pressure for greatest number of gametes that could
swim the fastest would work on sperm.
The end result are two very different gametes (heterogamy).
2. Disruptive selection (diversifying selection)-There is a
selection pressure for the two extremes, this causes an
increase for the traits at the extreme.
Ex- Suppose that gametes were the same size (isogamy). Two
selection pressures operating on the two types of gametes.
1. Selection pressure of storing food for future embryo would
work on eggs.
2. Selection pressure for greatest number of gametes that
could swim the fastest would work on sperm.
The end result are two very different gametes (heterogamy).
3. Stabilizing selection- In this case, the intermediate
phenotype is selected for and the extremes are selected
against. This reduces variation in the population.
3. Stabilizing selection- In this case, the
intermediate phenotype is selected for and the
extremes are selected against. This reduces
variation in the population.
i.e. Human birth weight is on the average 3-4 kg. It is
well known that the smaller the baby (>3-4 kg), the less
likely it will survive but it is also detremental to have
large babies and the survival rate decreases (<3-4 kg)
i.e. Human birth weight is on the average 3-4 kg. It
is well known that the smaller the baby (>3-4 kg),
the less likely it will survive but it is also
detrimental to have large babies and the survival
rate decreases (<3-4 kg).
It is possible to have variation in population that is stable and one
phenotype is not favored over another therefore the allelic
frequencies do not change. This may be due toa. the environment may be variable and one morph may do better
in one environment than the other
b. one morph may be better adapted to one time of the year more
than the other. The lady bird beetle has 2 morphs. The red is
much better as survival in the spring and winter. The black morph
is much better with survival in the summer and fall.
It is possible to have variation in population that is stable and one
phenotype is not favored over another therefore the allelic
frequencies do not change. This may be due toa. the environment may be variable and one morph may do better
in one environment than the other
b. one morph may be better adapted to one time of the year more
than the other. The lady bird beetle has 2 morphs. The red is
much better as survival in the spring and winter. The black morph
is much better with survival in the summer and fall.