©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
organic evolution exam 2 study guide
solutions
For allele frequencies to change there has to be: - ANSWER✔✔-variation (there have to be different
alleles)
Variation in a population comes from : - ANSWER✔✔-Mutation
Gene Flow
Once genetic variation has been established, what causes the allele frequencies in a population over
generations? - ANSWER✔✔-Natural selection
Genetic drift
More Gene Flow
Only natural selection causes : - ANSWER✔✔-adaptive evolution
Evolution by natural selection involves both ___ and _____ - ANSWER✔✔-chance and "sorting"
New genetic variations arise by chance
Page 1/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Beneficial alleles are "sorted" and favored by natural selection
Natural Selection acts on the _______ not the _______ - ANSWER✔✔-Phenotype, Genotype
phenotypic diversity is affected by : - ANSWER✔✔-1. Multiple Genes (=Quantitative traits)
2. Interactions between different genes
3. Trade-offs
example of multiple genes: - ANSWER✔✔-wheat color: Three separate genes (A, B and C)
Independently assorting
i.e., on separate chromosomes
Alleles show incomplete dominance (heterozygote is intermediate between the homozygotes)
Dominate alleles contribute additively to pigmentation
because of independent assortment and the additive effect of the dominant alleles, some colors are
more common than others
Quantitative Trait - ANSWER✔✔-When many genes, each behaving individually, contribute to a
phenotypic feature in a cumulative way, the feature is called a Quantitative Trait
More genes involved in the trait, the more ______ exists - ANSWER✔✔-variation
Page 2/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Patterns of Natural Selection in Quantitative Characters - ANSWER✔✔-Directional
Stabilizing
Disruptive (=diversifying)
In any species and at any point in time, all three types of selection may be acting.
Directional Selection - ANSWER✔✔-Phenotypes at one extreme die off or fail to reproduce and those at
the other extreme leave a higher number of offspring.
This shifts the average frequency distribution towards the favored extreme.
ex.Biston betularia- moths
White phenotype
Dark phenotype
Originally, the vast majority of peppered moths had light coloration. Widespread pollution - esp. soot -
covered the trees and the white moths became more obvious to predators.
Page 3/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Dark-colored moths flourished because of their ability to hide on the darkened trees.
They left more offspring
Stabilizing Selection - ANSWER✔✔-Individuals with extreme phenotypes die or fail to reproduce
resulting in populations of individuals with intermediate phenotypes.
Most common in stable, unchanging environments where selection has remained the same for years.
disruptive selection - ANSWER✔✔-extreme phenotypes become more frequent from generation to
generation because they survive to reproduce while individuals with intermediate phenotypes die or fail
to reproduce.Diversifying selection results in polymorphism (two or more different forms are common).
ex.)taurus scarab beetles-one shows head spines the other does not Males with elaborate horns or
antlers may attract more mates but die younger because they are costly to grow, make the animal
clumsy and more obvious to predators. Males without elaborate horns or antlers attract fewer mates but
live longer.
Example of Tracking Natural Selection Affecting Quantitative Traits - ANSWER✔✔-Use survivorship or
number of offspring as an approximate measure
ex) beak of finch-
Step 1: Capture weigh, measure, and identify hundreds of the birds and record their diets of seeds
Step 2: For the seeds the finches eat, measure seed size and seed hardness
Page 4/53
FIRST PUBLISH OCTOBER 2024
organic evolution exam 2 study guide
solutions
For allele frequencies to change there has to be: - ANSWER✔✔-variation (there have to be different
alleles)
Variation in a population comes from : - ANSWER✔✔-Mutation
Gene Flow
Once genetic variation has been established, what causes the allele frequencies in a population over
generations? - ANSWER✔✔-Natural selection
Genetic drift
More Gene Flow
Only natural selection causes : - ANSWER✔✔-adaptive evolution
Evolution by natural selection involves both ___ and _____ - ANSWER✔✔-chance and "sorting"
New genetic variations arise by chance
Page 1/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Beneficial alleles are "sorted" and favored by natural selection
Natural Selection acts on the _______ not the _______ - ANSWER✔✔-Phenotype, Genotype
phenotypic diversity is affected by : - ANSWER✔✔-1. Multiple Genes (=Quantitative traits)
2. Interactions between different genes
3. Trade-offs
example of multiple genes: - ANSWER✔✔-wheat color: Three separate genes (A, B and C)
Independently assorting
i.e., on separate chromosomes
Alleles show incomplete dominance (heterozygote is intermediate between the homozygotes)
Dominate alleles contribute additively to pigmentation
because of independent assortment and the additive effect of the dominant alleles, some colors are
more common than others
Quantitative Trait - ANSWER✔✔-When many genes, each behaving individually, contribute to a
phenotypic feature in a cumulative way, the feature is called a Quantitative Trait
More genes involved in the trait, the more ______ exists - ANSWER✔✔-variation
Page 2/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Patterns of Natural Selection in Quantitative Characters - ANSWER✔✔-Directional
Stabilizing
Disruptive (=diversifying)
In any species and at any point in time, all three types of selection may be acting.
Directional Selection - ANSWER✔✔-Phenotypes at one extreme die off or fail to reproduce and those at
the other extreme leave a higher number of offspring.
This shifts the average frequency distribution towards the favored extreme.
ex.Biston betularia- moths
White phenotype
Dark phenotype
Originally, the vast majority of peppered moths had light coloration. Widespread pollution - esp. soot -
covered the trees and the white moths became more obvious to predators.
Page 3/53
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
Dark-colored moths flourished because of their ability to hide on the darkened trees.
They left more offspring
Stabilizing Selection - ANSWER✔✔-Individuals with extreme phenotypes die or fail to reproduce
resulting in populations of individuals with intermediate phenotypes.
Most common in stable, unchanging environments where selection has remained the same for years.
disruptive selection - ANSWER✔✔-extreme phenotypes become more frequent from generation to
generation because they survive to reproduce while individuals with intermediate phenotypes die or fail
to reproduce.Diversifying selection results in polymorphism (two or more different forms are common).
ex.)taurus scarab beetles-one shows head spines the other does not Males with elaborate horns or
antlers may attract more mates but die younger because they are costly to grow, make the animal
clumsy and more obvious to predators. Males without elaborate horns or antlers attract fewer mates but
live longer.
Example of Tracking Natural Selection Affecting Quantitative Traits - ANSWER✔✔-Use survivorship or
number of offspring as an approximate measure
ex) beak of finch-
Step 1: Capture weigh, measure, and identify hundreds of the birds and record their diets of seeds
Step 2: For the seeds the finches eat, measure seed size and seed hardness
Page 4/53
