Transcript Chapter 23 outline

The Evolution of Populations
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Emphasizes the extensive genetic variation within
populations and recognizes the importance of
quantitative characteristics.
Modern Synthesis – comprehensive theory of
evolution that integrates discoveries and ideas from
many different fields, including paleontology,
taxonomy, biogeography, and, of course, population
genetics.
Modern synthesis emphasizes the importance of
populations as the units of evolution, the central role
of natural selection as the most important
mechanism of evolution, and the idea of gradualism
to explain how large changes can evolve as an
accumulation of small changes occurring over long
periods of time.
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Population – localized group of individuals
belonging to the same species
Species – a group of populations whose
individuals have the potential to interbreed
and produce fertile offspring in nature
Gene Pool – total aggregate of genes in a
population at any one time consisting of all
alleles at all gene loci in all individuals of the
population
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Hardy-Weinberg theorem – the frequencies of
alleles and genotypes in a population’s gene
pool remain constant over the generations
unless acted upon by agents other than
Mendelian segregation and recombination of
alleles
Hardy-Weinberg equilibrium – Mendelian
system has no tendency to alter allele
frequencies between generations
Hardy-Weinberg equation: p2 + 2pq + q2
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Very large population size.
No migration.
No net mutations.
Random mating.
No natural selection.
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Microevolution – Change in the gene pool on
the smallest scale
Genetic Drift – Change in the population’s
allele frequencies due to chance.
Bottleneck Effect – Genetic drift due to a
drastic reduction in population size.
Founder Effect – Genetic drift in a new colony.
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Natural Selection – Differential success in reproduction.
Gene Flow – When a population gains or loses alleles.
Mutation – Change in an organism’s DNA.
Polymorphic – If two or more distinct morphs are each
represented in high enough frequencies to be readily
noticeable.
Gene Diversity – Average percent of genetic loci that are
heterozygous.
Nucleotide Diversity – Measured by comparing the
nucleotide sequences of DNA samples from two
individuals and then pooling the data from many such
comparisons of two individuals.
Geographic Variation – Differences in gene pools between
populations or subgroups of populations.
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Balanced Polymorphism – Ability of natural selection
to maintain stable frequencies of two or more
phenotypic forms in a population. Two mechanisms:
Heterozygote Advantage – If individuals who are
heterozygous at a particular locus have greater
survivorship and reproductive success than any type
of homozygote, then two or more alleles will be
maintained at that locus by natural selection.
Frequency-Dependent Selection – The survival and
reproduction of any one morph declines if that
phenotypic form becomes too common in the
population.
Neutral Variation – Confers no selective advantage for
some individuals over others, i.e. fingerprints.
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Darwinian Fitness – contribution of an
individual to the gene pool of the next
generation relative to the contributions of
other individuals.
Relative Fitness – contribution of a genotype
to the next generation compared to the
contributions of alternative genotypes for the
same locus.
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Directional Selection – most common during
periods of environmental change or when
members of a population migrate to some new
habitat with different environmental conditions.
Diversifying Selection – occurs when
environmental conditions are varied in a way that
favors individuals on both extremes of a
phenotypic range over intermediate phenotypes.
Stabilizing Selection – acts against extreme
phenotypes and favors the more common
intermediate variants.
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Sexual Dimorphism – marked differences,
called secondary sexual characteristics, not
effected by reproduction
Intrasexual Selection – direct competition
among individuals of one sex for mates of the
opposite sex
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1. Evolution is limited by historical
constraints.
2. Adaptations are often compromises.
3. Not all evolution is adaptive.
4. Selection can only edit existing variations.