Transcript mechanisms for evolution

MECHANISMS FOR
EVOLUTION
CHAPTER 23
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Objectives
– State the Hardy-Weinburg theorem
– Write the Hardy-Weinburg equation and be able
to use it to calculate allele and genotype
frequencies
– List the conditions that must be met to maintain
Hardy Weinburg equilibrium
VOCABULARY
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POPULATION
SPECIES
GENE POOL
GENE FLOW
BOTTLENECK
EFFECT
FOUNDER EFFECT
HETEROZYGOTE
ADVANTAGE
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HYBRID VIGOR
STABILIZING
SELECTION
DIRECTIONAL
SELECTION
DIVERSIFYING
SELECTION
SEXUAL
DIMORPHISM
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POPULATION
– Localized group belonging to the same species
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SPECIES
– Naturally breeding group of organisms that
produce fertile offspring
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GENE POOL
– Total aggregate of genes in a population at any
one time
Most species are not evenly distributed over a
geographic range. Individuals are more likely
to breed with others from their population
center
HARDY – WEINBURG THEOREM
Describes a NON-EVOLVING population
 In the absence of other factors the
segregation and recombination of alleles
during meiosis and fertilization will not
alter the overall genetic make-up of a
population
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Imagine an isolated
wildflower population
with the following
characteristics
– Diploid with both pink
and white flowers
– Pink is dominant A and
white is recessive a
– There are 480 pink
flowers and 20 white
» 320 are AA
» 160 are Aa
(p + q)2 = 1
p+q=1
p2 + 2pq +q2 = 1
p2 = frequency of AA
 2pq = frequency of Aa
 q2 = frequency of aa
 Calculate q2 first
 There are 1000 alleles
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– AA -- 320 x 2/plant = 640
– Aa --160 x 1/plant = 160
800
– aa -- 20 x 2/plant = 40
– Aa – 160 x 1/plant =160
–
200
– Frequency of A = 80% and a = 20%
Condition for Hardy-Weinburg
 Large
population
 No net mutation
 Isolated population
 Random mating
 No natural selection
MICROEVOLUTION
LEADS TO
MACROEVOLUTION
CAUSES OF
MICROEVOLUTION
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GENETIC DRIFT
– BOTTLENECK EFFECT
– FOUNDER EFFECT
GENE FLOW – genetic exchange
between populations due to migration
 Mutation – a new mutation that is
transmitted in a gamete can immediately
change the gene pool
 NONRANDON MATING
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– Breed with other members of the
“neighborhood” promotes inbreeding
– Assortative mating – mate with others like
themselves
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NATURAL SELECTION
Variation within Populations
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Most heritable variation is measured by
– Quantitative characters (vary along a
continuum ie. Height) are polygenetic
– Discrete characters (pink or white) are
located on a single gene
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Polymorphism – two or more forms of a
discrete character are represented in a
population
GEOGRAPHICAL VARIATION
A cline is a graded change in some trait along a
geographical axis.
MODES OF SELECTION