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BIOC50H3 (31)
Lecture

Important Terms and Definitions

2 Pages
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Department
Biological Sciences
Course Code
BIOC50H3
Professor
Marc Cadotte

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Lecture 19
African elephants are poached for ivory; the proportion of the population that have tusks
is decreasing
By targeting older, larger fish, commercial fishing for cod has led to a reduction in the
age and size at which these fish mature
Evolution can be viewed as genetic change over time or as a process of descent with
modification
Evolution:
o A change in the genetic characteristics of a population over time
o Descent with modification-organisms gradually accumulate differences from their
ancestors
Natural selection: Individuals with particular adaptations tend to survive and reproduce at
a higher rate than other individuals
The genotype is the genetic makeup, and is represented by letters, one for each allele
Natural selection, genetic drift, and gene floe can cause allele frequencies in a population
to change over time
Phenotype- the observable characteristics of individuals that are determines by the
genotype
Directional selection: Individuals with one extreme of a heritable phenotypic trait (for
example, large size) are favoured
Stabilizing selection: Individuals with an intermediate phenotype are favoured
Disruptive selection: Individuals at both phenotypic extremes are favoured
Genetic drift occurs when chance events determine which alleles are passed to the next
generation
Some alleles may disappear, other may reach 100% frequency- fixation
Gene flow occurs when alleles are transferred from one population to another via
movement of individual or gametes
Natural selection is the only evolutionary mechanism that consistently causes adaptive
evolution
Adaptations are features of organisms that improve their ability to survive and reproduce
in their environments
Adaptive evolution-traits that confer advantages tend to increase in frequency over time
There are several constraints on evolution:
o Lack of genetic variation
o Evolutionary history
o Ecological trade-offs
Lack of genetic variation: If there is no beneficial allele, adaptive evolution at the gene
cannot occur
Evolutionary history: Natural selection works on the traits already existing in organisms
Ecological trade-offs: All organisms face trade-offs in allocation of energy and resources
to growth, reproduction and survival
www.notesolution.com

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Description
Lecture 19  African elephants are poached for ivory; the proportion of the population that have tusks is decreasing  By targeting older, larger fish, commercial fishing for cod has led to a reduction in the age and size at which these fish mature  Evolution can be viewed as genetic change over time or as a process of descent with modification  Evolution: o A change in the genetic characteristics of a population over time o Descent with modification-organisms gradually accumulate differences from their ancestors  Natural selection: Individuals with particular adaptations tend to survive and reproduce at a higher rate than other individuals  The genotype is the genetic makeup, and is represented by letters, one for each allele  Natural selection, genetic drift, and gene floe can cause allele frequencies in a population to change over time  Phenotype- the observable characteristics of individuals that are determines by the genotype  Directional selection: Individuals with one extreme of a heritable phenotypic trait (for example, large size) are favoured  Stabilizing selection: Individuals with an intermediate phenotype are favoured  Disruptive selection: Individuals at both phenotypic extremes are favoured  Genetic drift occurs when chance events determine which alleles are passed to the next generation  Some alleles may disappear, other may reach 100% frequency- fixation  Gene flow occurs when alleles are transferred from one population to another via movement of individual or gametes  Natural selection is the only evolutionary mechanism that consistently causes adaptive evolution  Adaptations are features of organisms that improve their ability to survive and reproduce in their environments  Adaptive evolution-traits that confer advantages tend to increase in frequency over time  There are several constraints on evolution: o Lack of genetic variation o Evolutionary history o Ecological trade-offs  Lack of genetic variation: If there is no beneficial allele, adaptive evolution at the gene cannot occur  Evolutionary history: Natural selection works on the traits already existing in organisms  Ecological trade-offs: All organisms face trade-offs in allocation of energy and resources to growth, reproduction and survival www.notesolution.com  Long-term patterns of evolution are shaped by large-scale processes such as speciation, mass extinction, and adaptive radiation  Species are groups of organisms whose members have similar characteristics and can interbreed  Speciation- the process by which one species splits into two or more species  Gene flow always acts to slow down or prevent speciation  Trophy hunting has caused directional selection www.notesolution.comLecture 19 African elephants are poached for ivory; the proportion of the population that have tusks is decreasing By targeting older, larger fish, commercial fishing for cod has led to a reduction in the age and size at which these fish mature Evolution can be viewed as genetic change over time or as a process of descent with modification Evolution: o A change in the genetic characteristics of a population over time o Descent with modification-organisms gradually accumulate differences from their ancestors Natural selection: Individuals with particular adaptations tend to survive and reproduce at a higher rate than other individuals The genotype is the genetic makeup, and is represented by letters, one for each allele Natural selection, genetic drift, and gene floe can cause allele frequencies in a population to change over time Phenotype- the observable characteristics of individuals that are determines by the genotype Directional selection: Individuals with one extreme of a heritable phenotypic trait (for example, large size) are favoured Stabilizing selection: Individuals with an intermediate phenotype are favoured
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