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T. Dobzhansky (geneticist). “Nothing in biology makes sense except in the light of evolution”. Adaptation. A genetically determined characteristic that influences an organism's ability to survive and reproduce in a particular environment. - PowerPoint PPT Presentation
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T. Dobzhansky (geneticist)
“Nothing in biology makes sense
except in the light of evolution”
Adaptation
A genetically determined characteristic that influences an organism's ability to survive and reproduce in a particular environment.
Characteristics can be morphological, behavioral, or physiological.
Evolution
• Is a genetic change in a population (not an individual) over time
• Ecologists look at phenotypic (physical changes), in most cases, because that is how we recognize populations.
• It is, in fact, changes in the genotype, or more specifically, the gene pool.
Allele Frequencies
The frequency of occurrence of alleles in a population.
If we use the simple one dominant and one recessive allele model, this can be demonstrated by:
p = frequency of the dominant allele
q = frequency of the recessive allele
Example
AA - 30 individuals
Aa - 20 individuals
aa - 50 individuals
p = 2(# individuals AA) + # individuals Aa 2(Total # individuals in population)
p + q = 1; therefore q = 1 - p
Example
p = 2(30) + 20 200= 0.4
p + q = 1; therefore q = 1 - 0.4 = 0.6
With these values, we can calculate the probability of what genotypes would be present in the next generation if this population were to mate randomly
Genotypic Frequencies
p2 = probability of AA
q2 = probability of aa
2pq = probability of Aa
p2 + 2pq + q2 = 1
Mechanisms for Evolutionary Change
Mutation
Genetic Drift (small population size)
Gene Flow (immigration and emigration)
Non-Random Mating
Natural Selection
Basic Tenet of Natural Selection
The most fit organisms (survivors) will reproduce and pass their genes
on to the next generation.
Hardy-Weinberg Equilibrium
In diploid, sexually reproducing organisms, phenotypes, genotypes and genes all tend to come to equilibrium in
populations in certain conditions are met
Hardy-Weinberg Equilibrium No Mutation
Large Population Size
No immigration or emigration
Random Mating
No Selection for Traits
Genetic Drift
• Random or chance events lead to a change in the genetic makeup of a population
• Limited to small populations
• “Bottleneck”
p = 0.7
Random event leads to loss of individuals
p = 0.33
Population will come to reflect surviving population
Effective Population Size (Ne)
The number of individuals actually participating in random mating.
This number is always smaller than the actual population size
- number of old- number too young- small number of one sex
Gene Flow
• Change in gene pool of a population from immigration or emigration.
• Founder Effect
Identification of Human Migration fromMitochondrial DNA
Steps for Natural Selection
• Variation occurs in every group of living organisms. Individuals are not identical in any population.
• Every population produces an excess of offspring.
• Competition will occur among these offspring for the resources they need to live.
Steps for Natural Selection
• The most fit offspring will survive.
• If the characteristics of the most fit organisms are inherited, these favored traits will be passed on to the next generation.
Common Types of Individual Selection
• Stabilizing selection
• Direction selection
• Disruptive selection
Figure 21.12
Figure 21.12
figure 21-12.jpg
Figure 21.13
Figure 21.13
Figure 21.14
Similarities in Adaptive Strategies
• Convergent Evolution – similar responses to similar environmental situations BUT not related evolutionarily
• Example – Fig. 2.9
!!!!!!!!!!VARIATION!!!!!!!!!!!
Properties of Fitness
• Fitness is a property of a genotype, not an individual or population.
• Fitness is specific to a particular environment. As the environment changes, so does the fitness of genotypes.
• Fitness is measured over one generation or more.
Outcomes of Selection
• Changes in Genetic Make-up of a Population
• Rise of new species – IF certain conditions met
Distribution of a Species
Allopatric Speciation
Geographic Barrier Splits Distribution
No longer interbreeding; therefore, no exchangeof genes and could be undergoing different selectionpressures
Over time, the gene pool of each group can become quit different
If two groups are brought back together anddo not interbreed, they are now two separate species
Distribution of a Species
Parapatric Speciation
Individuals move into a new habitat
If no interbreeding occurs between individualsin new habitat and those in the old, reproductiveisolating mechanisms can develop.
Isolating mechanism develops within the existing distribution of a species
Sympatric Speciation
Isolating mechanism develops within the existing distribution of a species
Sympatric Speciation
Reproductive Isolating Mechanisms
• Prezygotic mechanisms prevent fertilization or zygote formation. Temporal shifts - do not become reproductively
active at the same time. Behavioral shifts - do not recognize courtship
behaviors (female bird doesn't recognize the dance of a male).
Mechanical shift - change in reproductive structure making it physically impossible to mate.
Habitat shifts – populations live in the same regions but occupy different habitats/microhabitats.
Reproductive Isolating Mechanisms
• Postzygotic mechanisms zygote forms but
Does not complete development
Develops into a weak, unhealthy individual
Is sterile in either the F1 or F2 generation
Evolution of Interactions Among Species
Mimicry
• Batesian mimicry - a benign species resembles a noxious or dangerous species.
• Müllerian mimicry - both the mimics and the model are noxious or dangerous.
Coevolution
• Evolutionary change in one species results in a reciprocal response of another species
• Many examples – excellent one is diversification of flowering plants and insect pollinators
• Parasitism• Predator-Prey Interactions (including
herbivory)• Competition
• Other topics of note– Sexual selection– Kin Selection