Transcript Chapter 13- How Populations Evolve

Chapter 13- How Populations Evolve
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Artificial selection
Biogeography
Bottleneck effect
Comparative anatomy
Comparative embryology
Descent with modification
Directional selection
Diversifying selection
Evolution
Evolutionary adaptations
Fitness
Fossil record
Founder effect
Gene flow
Gene pool
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Genetic drift
Hardy-Weinberg equilibrium
Homologous structures
Microevolution
Modern synthesis
Molecular biology
Mutation
Natural selection
Neutral variation
Population
Population genetics
Sexual dimorphism
Species
Stabilizing selection
Evolution
• Change over time
• Darwin called evolution- descent with
modification until last paragraph of The
Origin of Species
Evolutionary adaptations
• Inherited traits that increase an organism’s
ability to survive and reproduce in a
particular environment
Fossil record
• Ordered specimens in layers of sedimentary
rock
– Gives an idea of when certain adaptations appear
– Younger fossils are on top of older ones
Biogeography
• Geographic distribution of species
Comparative anatomy
• Comparing body structures
– Homologous structures- features with similar structure
but a different function
• Due to similar ancestry
Comparative embryology
• Study of
structures
that appear
during
development
– Shows
common
ancestry in
vertebrates
Molecular biology
• Study of molecular basis of genes and gene
expression
– Universal genetic code= life is related
– Similar DNA and proteins= close relationships
Darwin’s Theory points:
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Overproduction
Competition
Variety
Adaptations
Natural selection
Speciation
Artificial selection
• Selective breeding of plants and animals
Natural selection
• Unequal reproductive
success
– Those that are better
adapted to the env are
more likely to survive,
reproduce
– Mechanism for evolution
Natural selection in action:
– Galapagos finches- avg. beak size differs in
wet vs. dry years
– Insecticide resistance- resistant insects
survive and reproduce, next generation more
are resistant
– Antibiotic resistance- similar to insecticide
resistance
– Industrial melanism- moth coloring due to
industrialization in England
Population
• Smallest unit that can evolve
• Group of individuals of the same species living in
the same place at the same time
• Population genetics- science of genetic change
in populations
Population vocab
– Modern synthesis- theory of evolution that
includes genetics
– Species- group of populations whose
individuals can reproduce and produce fertile
offspring
Gene pool
• Collection of genes (alleles) in
a population at any given time
– Frequency of alleles can change
• Microevolution- change in
gene pool over a few
generations
• Gene pools will remain
constant if the population isn’t
evolving – IMPOSSIBLE!!
Hardy-Weinberg Equilibrium
– Frequency of each allele in the gene pool will
remain constant unless acted on by other
agents
–
p2
+
2pq +
q2
=1
– freq. WW + freq. Ww + freq. ww = 1
– Used in human genetics to estimate how
many people carry alleles for certain inherited
diseases
5 conditions for H-W equilibrium
• Large population
• Pop. is isolated, no migration of individuals or gametes in
or out
• Mutations don’t alter gene pool
• Random mating
• All individuals are equal in reproductive success; natural
selection does NOT occur
• IMPOSSIBLE
Causes of microevolution
• Natural selection
• Genetic drift- change in gene pool due to change
– Bottleneck effect- random, drastic reduction of population size
(ex: flood, earthquake)
– Founder effect- colonization of a new location by a small # of
individuals (ex: birds fly to new island)
Causes of microevolution con’t
• Gene flow- genes move into or out of a
population (by fertile individuals or gametes)
• Reduces genetic differences between pop.’s
• Mutation- change in DNA, causes new alleles
– ** ultimate source of genetic variation
– Raw material for evolution
Variation
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Prevalent in most populations
Especially sexually reproducing species
Many traits are the result of several genes
Polymorphic- characteristic with 2 or more forms
– ABO blood type
• Can also happen in a cline- change in characteristic due
to geography
– As latitude increases, mammal/bird size increases
• Is measured in gene or nucleotide diversity
Variation con’t
• Produced by sexual recombination and
mutation
– Most of the time it’s harmful, occasionally it creates a better
variation
– Asexual org’s- mutation generates
– Sexual org’s- sexual recombination generates
How natural selection affects variation
• Heterozygote advantage- have greater reproductive
success
– Ex: malaria/sickle-cell
• Balanced polymorphism- ability of natural selection to
maintain 2 or more phenotypes
• Neutral variation- no selective advantage (human
fingerprints)
• Endangered species have reduced variation
– Why? Small gene pool
Fitness
• Relative contribution to gene pool of next generation
– More fit- reproduce more have well-adapted young that
reproduce
– Fittest individual- passes most genes to next generation
Outcomes of natural selection
Outcomes of natural selection
– Stabilizing- favors intermediates
• Occurs in stable env’s
• Prevails most of the time in
populations
– Directional- favors an extreme
phenotype
• Occurs during env. change or
when there is migration to new
habitat
– Diversifying- favors both
extremes
• Can lead to balanced polymorphism
• Occurs when habitat has 2 different
env conditions
Natural selection DOES NOT
produce perfection, due to:
• Historical constraints
– Need to use already existing structures
• Compromising for adaptations
– Blue-footed booby- fast in water, clumsy on land
• Not all evolution is adaptive
– Chance happens, ex: bottleneck (could remove good genes)
• Selection is only on existing variations
Sexual selection may produce
sexual dimorphism
• Sexual dimorphism- distinction between secondary sex
characteristics in males and females
– Plumage, antlers, dances, manes
– Intrasexual selection- fighting for females
– Intersexual selection- mate choice, impressing other sex by
dance, feathers etc
• Many times it’s not advantageous to stick out to predators but it’s necessary
for passing on genes