Unit 4: Mechanisms of Evolution
Animations
Study Guide
Chapter 23
The Evolution of Populations
Review
A
is a
localized
group of individuals of a species.
Natural selection acts on individuals, but
evolve,
based on
variations
that are inherited over generations.
As a population evolves, its heritable variation is reflected in change of
and
frequencies.
A non-evolving population reaches the
equilibrium
due to Mendelian
of alleles.
At Hardy-Weinberg equilibrium, the distribution of 2
p
and
q
in a population can be modeled by these
equations:
The
frequencies are described by
p
+
q
= 1, where
p
is the dominant allele frequency and
q
is the recessive allele frequency.
The
frequencies are described by
p
2
+ 2
pq
+
q
2
= 1, where
p
2
and
q
2
are frequencies of the homozygous genotype and 2
pq
is the frequency of the heterozygous genotype.
Natural populations may
if conditions deviate from the Hardy-Weinberg model.
Genetic
in small populations tends to
genetic variation. In very small populations the
effect
can contribute to severe loss of genetic diversity.
Gene
from the movement of individuals or gametes between populations can affect allele frequencies and tends to
genetic differences between
populations.
is the basis for
natural
selection, and results in unequal reproduction of alleles.
Natural
selection
is the major mechanism that drives adaptive
.
Causes of Evolutionary Change:
Natural selection in sexually reproductive organisms often leads to behaviors such as
selection and
selection.
Heterozygotes sometimes may possess greater
than homozygotes and preserve a recessive allele in a population due to
advantage.
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