Download Populations are units of evolution

13.6 to 13.8

A group of interacting
individuals belonging
to one species and
living in the same
geographic area
Population

A group whose
members possess
similar anatomical
characteristics and have
the ability to interbreed
Species

The study of genetic
changes in populations; the
science of
microevolutionary changes
in a population
Population Genetics

A comprehensive theory of
evolution that incorporates
genetics and includes most
of Darwin’s original ideas,
focusing on populations as
the fundamental units of
evolution (individuals don’t
evolve – populations do)
Modern Synthesis
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All of the alleles for all of
the loci in all individuals in
a population
Each allele has a frequency
in the population
Example: you have a wild
boar population in which 50
percent of the alleles for a
particular gene are
dominant (B) and 50
percent of the alleles for
the gene are recessive (b).
Gene Pool
Example
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
A change in a
populations gene pool
over a succession of
generations;
evolutionary changes
in species over
relatively brief periods
of geologic time
Change in the allele
frequency over time
Microevolution
example
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Named for 2 men who
figured out that the
shuffling of genes that
occurs during sexual
reproduction, by itself,
cannot change the overall
genetic make-up of a
population
p + q = 1 (p = dominant
allele frequency / q =
recessive allele frequency)
p2 + 2pq + q2 = 1 ( p2 =
homo dominant; 2pq =
hetero; q2 = homo
recessive)
Hardy Weinberg
Equilibrium
1.
2.
3.
4.
5.
Large population
No migration in or out
Mutations do not alter
gene pool
Random mating
Natural selections
does not occur (all
have equal chance to
survive)
5 Conditions of Hardy
Weinberg
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About 1 in 10,000 babies
born in the US have PKU
How many people are
carriers?
First step: calculate q2
(individuals with PKU /
homo recessive)
◦ q2 = 1/10,000 = 0.0001

Solve for q (the frequency
of the recessive allele in
the population)
◦ q = q2 = 0.01

Use the equation “p +
q = 1” to solve for p.
◦ p = 0.99

Use the equation “p2 +
2pq + q2 = 1” and
solve for carrier
genotype.
◦ 2pq = 2(.99)(.01) = .0198
◦ ~2% of the population are
carriers
PKU – autosomal
recessive trait
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You have sampled a
population in which you
know that the percentage of
the homozygous recessive
genotype (aa) is 36%. Using
that 36%, calculate the
following:
◦ The frequency of the "aa"
genotype.
◦ The frequency of the "a" allele.
◦ The frequency of the "A" allele.
◦ The frequencies of the
genotypes "AA" and "Aa."
◦ The frequencies of the two
possible phenotypes if "A" is
completely dominant over "a."
Try it yourself
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q2 = .36
q = .6; frequency of “a”
allele is 60%
p = .4; frequency of “A”
allele is 40%
p2= .16; frequency of AA
is 16%
2pq = .48; frequency of
Aa is 48%
Frequency of A
phenotype is 64%
Frequency of a
phenotype is 36%
Answer