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Art
Unit 4: Mechanisms of Evolution
The Evolution of Populations
Review
Natural selection acts on individuals, but
evolve, based on genetic
variations,
the change in genetic makeup of a
population
over time is called
.
A
is a
localized
group of individuals that are capable of
interbreeding
and producing
offspring.
As a population evolves, its
and
frequencies change. Such
change can be analyzed by comparing it to a non-evolving population.
A non-evolving population reaches the
equilibrium due to
Mendelian
of alleles, under five idealized conditions:
Extremely
population size.
No gene
due to migration.
No
.
mating.
No natural
.
Mendelian inheritance preserves
frequencies in a population, resulting in constant
variation.
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.
Mutation
and
sexual
produce the variation that makes
evolution
possible.
Genetic
in small populations result 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.
Selection favors certain
by acting on the
of individuals.
selection
favors individuals at one end of the phenotypic range.
selection
favors individuals at both extremes of the phenotypic range.
selection
favors intermediate phenotypes.
Summary.
Heterozygotes sometimes may possess greater
than homozygotes and preserve a recessive allele in a population due to
advantage.
In many species
are choosy in selecting their mates, resulting in
sexual
. This is called
selection, or
choice.
selection is the
competition
among males for access to mates, often at the peril of their own survival.
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