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Population Genetics and Speciation
Section 1
Bellringer
Imagine that you are in charge of a
goat ranch. The cost of fencing is high,
so you must implement a breeding
program that will produce shorterlegged goats within the next 20
years. Write down how you would
meet this goal.
Population Genetics and Speciation
Section 1
Key Ideas
• How is microevolution studied?
• How is phenotypic variation
measured?
• How are genetic variation and change
measured?
• How does genetic variation originate?
Population Genetics and Speciation
Section 1
Population Genetics and Speciation
Population
Section 1
What kinds of variation can
Geneticsbe seen in this photograph?
• Charles Darwin knew that heredity
influences characteristics, but he did know
about genes.
• We can now study and predict genetic
variation and change that underlie
evolution.
• Microevolution is evolution
at theinlevel
of
variation
flower
color and plant height
genetic change in populations.
Population Genetics and Speciation
Section 1
Population Genetics, continued
• Microevolution can be studied by observing
changes in the numbers and types of alleles
in populations, called population genetics.
• The study of genetics and evolution are
advancing together.
• The link from microevolution to
macroevolution—speciation—can be
studied in detail.
Population Genetics and Speciation
Section 1
What do we now know about heredity
that Darwin did not know?
We know about genetics, such as
how genotype relates to phenotype.
Visual Concept: Population
Eye colorSection
is a 1
polygenic
Phenotypic Variation
character.
• The variety of phenotypes that exists
for a given
Different
characteristic depend on how many
genes genes
affect
it.
control different
• Polygenic characters are influenced
by several
pigments,
genes. Examples include human eye color and
which
combine
height.
to produce
• Biologists study polygenic phenotypes
by
various
shades
measuring each individual in the
population
and
then analyzing the distribution of
ofthe
blue, green,
measurements.
or brown.
Population Genetics and Speciation
Population Genetics and Speciation
Section 1
Visual Concept: Single Allele, Multiple Allele
and Polygenic Traits
Population Genetics and Speciation
Section 1
Phenotypic Variation, continued
• A distribution is an overview of the
relative frequency and range of a set of
values.
• Often, some values in a range are more
common than others.
• A normal distribution, or bell curve, is
one that tends to cluster around an
average value in the center of the range.
Population Genetics and Speciation
Normal Distribution
Section 1
Why do polygenic
characters vary so
much?
How do the number of genes for a character relate to
because
many
unique
its variation?
The more genes that affect a character, the more
combinations
of alleles
variations
there can be.
are possible
Population Genetics and Speciation
Section 1
Measuring Variation and Change
• The particular combination of alleles in a
population at any one point in time makes up a
gene pool.
• Genetic variation and change are measured in
terms of the frequency of alleles in the gene pool
of a population.
• A frequency is the proportion or ratio of a group
that is of one type. To study genetic change, the
frequency of each allele in a population can be
tracked over time.
Population Genetics and Speciation
Section 1
What is the main measure of
genetic variation?
frequency of alleles
Visual Concept: Population
and Gene Movement
Population Genetics and Speciation
Genotype Frequencies Vs. Allele
Frequencies
Is the dominant
allele always the
most frequent?
No. Even if an
allele is
dominant, it may
not be the most
frequent allele in
a population.
Section 1
Population Genetics and Speciation
Section 1
Why is mutation so
important?
Sources of Genetic Variation
• Evolution cannot proceed if there is no
variation. The major source of new alleles
in natural populations is mutation in germ
cells.
• Mutation generates new alleles at a slow
rate.
• Only mutations in germ cells (egg and
sperm) are passed on to offspring.
• Visual
because it is the source
of variation in
populations
Population Genetics and Speciation
Section 1
Genotype Frequencies
• (frequency of EE) + (frequency of Ee)
+ (frequency of ee) = 1
• (frequency of E) + (frequency of e) =
1
• What is the sum of all allele
frequencies for any one gene?
• 1 or 100%
Population Genetics and Speciation
Section 1
Exit Question
The sum of all allele frequencies in a
population at any time is called ______.
A. polygenic
B. genotype frequency
C. a phenotypic variation
D. a gene pool
Population Genetics and Speciation
Section 1