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The Theory of Evolution – Mechanisms for Evolution
Populations Genetics and Evolution
 _____________________ evolve, not ____________________
 Natural selection acts on the ___________ of ________________
 Gene pool
 All of the _________ in a pop
 Allelic frequency
 percentage of any _____________ allele in the _____ pool
 Calculating Allelic Frequency
 Same way a baseball player calculates batting average
 Add up all of the alleles/total # alleles; Fig. 15.11
 Genetic Equilibrium
 ______________ of alleles remains the __________over generations
Changes in Genetic Equilibrium
 Any factor that affects____________ in a gene pool can change ____________ frequencies =
disruption in equilibrium = ________________
 Mutations – can be ____________ or _____________
 _______________________
 Genetic drift
 The _______________ of allelic frequencies by ____________ events
 Can greatly affect _________ populations
 Only genes ________________ to pass on to offspring
 Found in humans that have become isolated
 Amish population in Lancaster County, Pennsylvania
 Pop = 12,000
 One of the original founders had the recessive allele for short arms
and legs and extra fingers and toes. Fig. 15.12
 Today 1 in 14, general pop of US 1 in 1000
 Gene Flow
 _____________________ of individuals _________ and out of a populations
 Leave a pop = _________ of genes in gene pool
 Enter a pop = ________ genes in gene pool
Natural Selection acts on Variations
 ____________ have variations
 Eye color, height, skin color
 Some variations ____________________ or _____________ an organism’s chance of
___________________ in an environment
 3 types of natural selection that act on variation
1. Stabilizing Selection
 Favors _________________ individuals in a pop
 Ex: spider size
 Too big = predators can find easily; Too small =
can’t get to food; Average = more likely to survive,
reproduce and pass on genes
2. Directional selection
 Favors one of the _________________ variations of a trait
 Ex:
woodpecker beak size
 Only those w/ long beaks can reach the bugs that live deep in the
tree

3.
Long beaks would be an advantage over short beaks or average size
beaks
Disruptive Selection
a. Individuals w/ ___________ ___________ of a trait’s variation are
selected.
i. Ex: marine limpets
1. Color from white, to tan, to dark brown
a. Live attached to rocks which are light and
dark; Both the white and dark brown are
camouflaged; Birds easily see tan
The Evolution of Species
 Speciation
 Occurs when members of __________ populations no longer _____________ to produce
fertile ___________
 Creates new ____________
 Geographic Isolation
 ____________ ____________ divides a population; Examples?
 Reproductive Isolation
 Occurs when formerly interbreeding organisms can no longer mate and produce fertile
offspring
 Genes are so different that fertilization or the production of a fertile offspring does
not occur
 Mating times differ
 Polypoidy
 Individual or species contains a _______________ of the normal set of c’somes
 Caused by mistakes during cell _______________
 May result in immediate reproductive isolation
 Speciation Rates
 Rate at which new species arise
 Gradualism
 _______________ change of adaptations; Ex: sea lilies
 Punctuated Equilibrium
 Occurs _____________, in rapid bursts
 Long periods of genetic __________________________ in between
Patterns of Evolution
 Occur throughout the world
 Support evolution
 Divergent Evolution
 Where species become _____________________ from each other
 Based on needs of particular environment
 Adaptive Radiation, example
 An _________________ species evolves into an array of species to fit a number of
_____________ habitats
 Ex: Darwin’s finches, honeycreepers
 Convergent Evolution
 __________________ related organisms evolve similar traits
 Share similar _________________________ ___________________
 Ex: shark, penguin, dolphin
 Fish, bird, mammal
 Why do they look similar?