Download Population Genetics

Population Genetics
Evolution by Natural Selection
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Evolution is ______________________________ (through several generations).
 Darwin
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Those individuals with ____________________ characteristics survive
and pass on their traits to the next ____________________
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Population gradually includes more individuals with
__________________ characteristics.
Gene Variation in Nature
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Polymorphism
 A gene with more than one allele is _______________________.
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Natural populations tend to have more polymorphic genes than can be
accounted for by ______________________.
Before Hardy-Weinberg
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Population Genetics - Study of properties of genes in populations.
 _______________________ inheritance was widely accepted.
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New genetic variants would quickly be ______________________.
 ______________________ had not yet been discovered.
SCIENTISTS COULD NOT ANSWER:
 Why don’t recessive traits ______________________after a while?
Hardy-Weinberg Principle
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Hardy-Weinberg – Two scientists came up with an explanation at the same time
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Original proportions of genotypes in a population will remain _______________from
generation to generation
Five Assumptions:
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Population is ___________________________
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Mating is __________________________
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No ___________________
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No ______________________
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No __________________ occurring
Calculate Genotype Frequencies
To find allele frequencies,let:
T=frequency of _________________ allele
t=frequency of __________________ allele
T + t = 1 (100% of alleles in population)
Frequency of homozygous recessive individuals (______) in the population is:
t x t = t2
Frequency of ________________ allele (t) in the population is:
t = √ t2
Frequency of ____________________ allele (T) in the population is:
T=1-t
Agents of Evolutionary Change
1. Mutation
 Mutation rates are generally so ________________ that they have
_____________ effect on Hardy-Weinberg proportions of common alleles.
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Ultimate source of genetic __________________.
2. Gene Flow
 ____________________ of alleles from one population to another.
Tend to ___________________ allele frequencies.
3. Genetic Drift
 Frequencies of particular alleles may change by _____________________.
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Important in _______________ populations.
 __________________ Effect - Few individuals found (start) new
population (small allelic pool).
 __________________ Effect - Drastic reduction in population, and
gene pool size.
4. Selection
 Artificial - Breeders exert ___________________.
 Natural - ___________________ exerts selection.
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Variation must exist among individuals.
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Variation must result in differences in numbers of viable offspring
produced.
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Variation must be genetically inherited.
 Natural Selection is a process, and Evolution is an outcome.
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Selection Pressures:
 Avoiding Predators
 Matching Climatic Condition
 Pesticide Resistance
Evolutionary Forces Maintaining Polymorphism
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Adaptive Selection Theory
 Heterogeneous environments produce many alleles.
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Neutral Theory
 Balance between mutation and genetic drift.
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Gene Flow versus Natural Selection
 Genetic drift may decrease frequency of an allele favored by selection.
Forms of Selection
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Disruptive Selection
 Selection eliminates intermediate types.
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Directional Selection
 Selection eliminates one extreme from a phenotypic array.
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Stabilizing Selection
 Selection acts to eliminate both extremes.
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Fitness - Number of surviving offspring passed to the next generation.