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Transcript
THE EVOLUTION OF
POPULATIONS
CHAPTER 23
POPULATIONS

Localized group of individuals belonging to the
same species

Species – group of individuals who have the
potential to interbreed and produce fertile
offspring

Similarities in individuals are
o
Morphological – structural
o
Physiological – metabolic activities
o
Behavioral – similar responses to same stimuli
Gene Pool

Total aggregate of genes in a population at any
one time

Nearly all genes in available pool have two or
more slightly different molecular forms – alleles

In closed population, only mutation brings about
changes to the gene pool
Genetic Variation

Difference in genes or other DNA segments among
individuals of the same population

Genotype is inherited

Phenotype is the environmental influence on
genotype

Average heterozygosity – average percent of loci
that are heterozygous; measure of the relative
age of a specific population

Variation between populations often due to
geographic variations
Genetic Variation

Sources of variation
o
Formation of new alleles through mutation
o
Altering of gene number and position due to errors
in meiosis
o
Rapid reproduction rate increases potential for
variation
o
Sexual reproduction shuffles genes more
effectively than asexual
Hardy Weinberg Equilibrium

Idea that allele frequency is constant from
generation to generation

Used to assess whether a population is evolving at
a specific locus by determining what the
population would be like if it were NOT evolving
at that locus

Scenario created is compared to actual
population; no change – no evolution; change –
evolution is occurring
Hardy Weinberg Equilibrium

All 5 conditions must be met for there to be no
evolution occurring:
1.
No mutations
2.
Random mating
3.
No natural selection
4.
Extremely large population size
5.
No gene flow
Altering Allele Frequencies in a
Population

Natural Selection – only mechanism that
consistently causes adaptive evolution

Genetic Drift – chance events that change allele
frequencies

Gene Flow – transfer of alleles into or out of a
population