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species
a group of similar organisms who have the potential to interbreed to produce fertile offspring.
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Population
all members of a single species in same place at same time
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Population genetics
diversity as allele frequencies.
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Variations
changes in allele frequencies
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Macroevolution
species change from one species to another
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Microevolution
changes in allele frequencies within a population
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gene pool
all alleles of the population.
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adaptive radiation
the emergence of numerous species from a common ancestor
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Hardy-Weinberg equation
(p2 + 2pq + q2 = 1.0); used to measure changes in gene frequencies over time within a population
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p2
frequency of the homozygous dominant genotype within gene pool
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2pq
frequency of the heterozygous genotype within gene pool
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q2
frequency of the homozygous recessive genotype within gene pool
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gene frequency calculation
to determine gene frequency, calculate its percent from the total number of alleles in the population
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there are 100 wolves
G grey
g white
the frequency of the G allele is .6
how many wolves are grey?
- p + q = 1 so q is .4
- p2 + 2pq + q2= 1.0
- q2 is the number of white wolves, p2 is number of dominant grey wolves, so p2+ 2pq will be the total number of grey wolves (2pq is heterozygous so those wolves will be grey)
- p2= .36
- 2pq = 2 (.6*.4) =2(.24) = .48
- .36 + .48 = .84; so 84 wolves are grey
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Hardy-Weinberg equation predicts that no change (evolution) will occur in a population if the following five conditions are met
- (1) Mating is random.
- (2) The population is isolated (no gene flow)
- (3) no natural selection
- (4) Mutations do not alter the gene pool.
- (5) The population is large.
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agents of evolutionary change
- 1. natural selection
- 2. genetic drift
- 3. mutation
- 4. gene flow
- 5. non-random mating
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natural selection
the mechanism that brings about adaptation to the environment as evolution occurs
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Genetic drift
a change in gene frequencies due to sampling error. In actual populations this may be due to the "founder effect" or after a disaster the "bottleneck effect".
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Mutations
changes in the genetic code
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Gene flow
gain or loss of genes from a gene pool due to movement of individuals
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Nonrandom mating
sexual selection
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founder effect
a small population is more apt to undergo genetic drift- high allele frequency changes by chance
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bottleneck effect
occurs when a majority of genotypes are prevented from participating in the production of the next generation due to extreme natural or human interference
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3 types of natural selection
- stabilizing selection
- directional selection
- disruptive selection
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stabilizing selection
- occurs when an intermediate phenotype can improve the adaptation of the population to those aspects of the environment that remain constant. the intermediate phenotype is favored
- ex. human birth weight; infants with intermediate weight have better chance at survival
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directional selection
- occurs when an extreme phenotype is favored, and the distribution curve shifts in that direction. changes the average phenotype of a population over time
- ex. the modern horse shows a gradual increase in body size as the environment changed from forest to grassland
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disruptive selection
- found when two ore more extreme phenotypes are favored over any intermediate phenotype
- ex. snails have wide habitat range; in low vegetation light banded snails are more prevalent, in forested areas, dark shells are more prevalent: so there are 2 distinct phenotypes in the population
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Theory of Punctuated Equilibrium
- proposed by Stephen Jay Gould and Niles Eldridge;
- suggests that evolution may be characterized by abrupt "starts and stops"; species may remain unchanged for long periods of time and then experience rapid evolution perhaps stimulated by catastrophic events;
- as opposed to Darwin's gradualistic model of evolution.
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Morphological (structural) traits
diagnostic traits: distinct physical characteristics
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Common Ancestry
A common ancestor for two or more different groups. It does not rely only on morphology to define a species
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reproductive isolating mechanisms
- inhibit gene flow
- 2 types: prezygotic and postzygotic
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prezygotic isolating mechanisms
- Habitat Isolation: 2 species separated by physical barrier
- Temporal Isolation: 2 species live in same area but don’t mate at the same time
- Behavioral Isolation: rituals that prevent one species from mating with another
- Mechanical Isolation: reproductive structure or other parts prevent mating
- Gamete Isolation: the gametes are incompatible; sperm wont get to the egg, or cant penetrate the egg, the egg may not recognize the sperm
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Postzygotic Isolating Mechanisms
- Postzygotic Isolating Mechanisms; if the zygote has formed
- hybrid inviability: zygote not viable; dies
- hybrid sterility: sterile adult
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speciation
making a species
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allopatric
- new species result because of geographical barriers
- adaptive radiation is a type of allopatric speciation
- allo-away, patric- country
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sympatric speciation
- species develops without geographical barrier
- one population develops into two or more with genetic variation
- polyploidy is a type of sympatric speciation in plants
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convergent evolution
similar trait evolves into two unrelated species as a result of exposure to similar enviroments
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