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Midterm

study guide for term test 2


Department
Biology
Course Code
BIO120H1
Professor
Jean Jiang Nash
Study Guide
Midterm

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Chapter 6
Inspiration to Charles Darwin: Galapagos archipelago, noticed that many
organisms living in the archipelago had different forms on different islands.
Original colonists: from South America
The archipelago is relatively dry. The el Nino brought increased rainfall and
increased vegetation, and the La nina brought drought again.
The environment influences phenotypes, not genotypes.
Phenotypic plascticity: the capacity of an individual to exhibit diff responses to its
environment.
Alleles are different forms of a particular gene.
Pleiotropy- effects of a single gene on multiple traits (ex: daf-2 in worms)
Many phenotypic traits show continuous variation (bell curve) like height.
The process of evolution has three main ingredients: variation among individuals,
inheritance of that variation, and differences in survival and reproductive success
related to that variation (fitness)
Example in text: California citrus pest some individuals in the pop. had alleles
endowing cyanide resistances, and when the pests were first sprayed with cyanide, the
organisms that did not have cyanide-resitant alleles, dies, but eventually the
population of those individuals who were cyanide-resitant increased, and so in turn
cyanide became useless after a while.
Sometimes the environment can influence phenotypes directly, and bring changes
in an individual that improves its relationship with the environment. This is referred
to as acclimatization- meaning the changes are beneficial but they are not adaptations.
Example in textbook: adapted the presence of a parastoid fly b/c of choosy
females.
Selection can influence the distribution of traits in a pop in 3 ways:
1.stabilizing selection- when individuals with average phenotypes have a
higher reproductive success than those with extreme phenotypes.
2.Directional selection- when the fittest individuals have an extreme
phenotype this shifts the distribution of phenotypes toward a new optimum,
then it is stabilized.
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3.Disruptive selection- when individuals with extreme phenotypes at either
end of the population distribution have higher fitness than individuals with
average phenotypes. This tends to increase genetic and phenotypic variation.
(though it is uncommon)
Example in textbook: industrial melanism peppered moth demonstrates genetic
change in response to darkened branches to avoid predation (camoflauge) illustrates
natural selection and evolutionary response over a short period of time.
Population genetics: method for predicting changes in gene frequency in response
to selection (the potential for evolution exists in all populations).
Example: cactus wren has no source of water, so must avoid gaining too much
heat from its environment. only live in Arizona desert. The orientation of the cactus
wren changes seasonally, so the nest is facing away form the cool winds in winter, and in
the summer, is facing toward the cool wind.
Reaction norm: observed relationship b/w the phenotype and the environement.
Example: heat energy heat accelerates most life processes. The butterfly grow faster
at high temperatures. However, different environments differ in this relationship.
Examples of acclimization: growing thicker fur, producing smaller leaves,
increasing number of red blood cells, and producing enzymes that remain fluid at diff
temperatures.
Process of modifying the body’s structure and metabolic machinery. (is reversible!)
However, increased tolerance to one extreme brings reduced tolerance to another.
Textbook example: creoste bush change temperature optima with seasons. Their
acclimization results from changes in the viscosity of the membranes directly involved in
photosynthesis.
A species capacity for acclimization may reflect the range of conditions in its
environment.
Developmental responses: when the attribute of the indivudal is modified for a
long time, even its whole lifetime. Example: African grasshopper change colours with
response to seasons to hide from predators this change is irreversible!
Genotype-environment interaction when a genotype performs better in one
environment than the other. these relationships can be revealed by reciprocal
transplant experments.
An example of the experiment: the growth rate of fence lizards reveal both genetic
determination and phenotypic plasticity. When there are fewer resources, lizards cannot
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