evolution of populations genes & variation--what causes genetic variation in populations?
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Evolution of PopulationsEvolution of Populations
Genes & Variation--What causes Genetic Variation
in Populations?
Genes & Variation--What causes Genetic Variation
in Populations?
Gene Pools and Allele Frequencies
Gene Pools and Allele Frequencies
What is a gene pool?
(All of the genes and information from all members of a particular species)
What are Allele Frequencies?
(How many times that allele occurs in the gene pool---eg. Black fur B = 40%)
What is a gene pool?
(All of the genes and information from all members of a particular species)
What are Allele Frequencies?
(How many times that allele occurs in the gene pool---eg. Black fur B = 40%)
Sources of Genetic Variation
Sources of Genetic Variation
Mutations
Gene Shuffling -- 23 chromosomes can produce 8.4 million different combinations of genes
Crossing Over -- Further, “Shufffles the deck” Producing more combinations
Mutations
Gene Shuffling -- 23 chromosomes can produce 8.4 million different combinations of genes
Crossing Over -- Further, “Shufffles the deck” Producing more combinations
Single Genes & Polygenic TraitsSingle Genes & Polygenic Traits
Single Gene Traits
AA, Aa, aa
Polygenic TraitsAABBCC, AaBbCc(3 Genes)-------->
Single Gene Traits
AA, Aa, aa
Polygenic TraitsAABBCC, AaBbCc(3 Genes)-------->
Natural Selection on Single gene Traits
Natural Selection on Single gene Traits
Can Lead to changes in the Allele Frequencies and
consequently----> Evolution
Example--Black and brown lizards
Red (mutation) doesn’t survive as well on a dark background
Can Lead to changes in the Allele Frequencies and
consequently----> Evolution
Example--Black and brown lizards
Red (mutation) doesn’t survive as well on a dark background
Natural Selection on Polygenic traits
Natural Selection on Polygenic traits
Can affect the distributions of phenotypes in 3 ways---
1) Directional selection 2) Stabilizing selection 3) disruptive selection
Can affect the distributions of phenotypes in 3 ways---
1) Directional selection 2) Stabilizing selection 3) disruptive selection
Stabilizing Selection-->Selects for the
average form
Stabilizing Selection-->Selects for the
average form
Example of Genetic DriftExample of Genetic Drift
An example is the frequency of total color-blindness among the inhabitants of Pingelap, an island in Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for achromatopsia.
An example is the frequency of total color-blindness among the inhabitants of Pingelap, an island in Micronesia. In approximately 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for achromatopsia.
After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of the population has complete achromatopsia.
After few generations, the prevalence of achromatopsia is 5% of population and 30% as carriers (by comparison, in the United States, only 0.003% of the population has complete achromatopsia.
Amish polydactyl (6 fingered) Achondroplastic Dwarf
Amish polydactyl (6 fingered) Achondroplastic Dwarf
Evolution vs. Genetic Equilibrium
Evolution vs. Genetic Equilibrium
Evolution = Genetic Change What does Genetic Equilibrium
= ?
NO CHANGE ! POPULATIONS WOULD STAY THE SAME, “IN EQUILIBRIUM”
Evolution = Genetic Change What does Genetic Equilibrium
= ?
NO CHANGE ! POPULATIONS WOULD STAY THE SAME, “IN EQUILIBRIUM”
Conditions for Equilibrium (Hardy--
Weinberg)
Conditions for Equilibrium (Hardy--
Weinberg) What would the conditions
have to be for no change? ie. No Evolution
1. No mutation 2. No natural selection 3. Large population 4. All members of the
population breed
What would the conditions have to be for no change? ie. No Evolution
1. No mutation 2. No natural selection 3. Large population 4. All members of the
population breed
5. Random mating 6. everyone produces the
same number of offspring 7. no migration in or out of
the population
5. Random mating 6. everyone produces the
same number of offspring 7. no migration in or out of
the population
Isolating MechanismsIsolating Mechanisms
GEOGRAPHIC REPRODUCTIVE
BEHAVIORAL TEMPORAL
GEOGRAPHIC REPRODUCTIVE
BEHAVIORAL TEMPORAL
GEOGRAPHIC ISOLATIONGEOGRAPHIC ISOLATION
Leads to--> Reproductive Isolation
Leads to--> Reproductive Isolation
REPRODUCTIVE ISOLATIONREPRODUCTIVE ISOLATION
Species can no longer reproduce with the, “New” species
Eg. 2 species of fruitflies
Guava or Banana?
The evolution of different mating location, mating time, or mating rituals:
Species can no longer reproduce with the, “New” species
Eg. 2 species of fruitflies
Guava or Banana?
The evolution of different mating location, mating time, or mating rituals:
TEMPORAL ISOLATIONTEMPORAL ISOLATION
Mating at different times of the year
Other frogs-- Green frogs-->
April Bullfrogs--> June
Mating at different times of the year
Other frogs-- Green frogs-->
April Bullfrogs--> June
BEHAVIORAL ISOLATIONBEHAVIORAL ISOLATION
Courtship rituals--(Dances, Flashes,)
Food preferences
Courtship rituals--(Dances, Flashes,)
Food preferences