BIO120H1 Chapter Notes - Chapter Lab 2: Phenotypic Trait, Stereo Microscope, Optical Microscope

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27 Nov 2018

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BIO120: Adaptation and Biodiversity Lab Manual (Chapter 2
Phenotypic Variation)
In association with Lab 2 and Lab Quiz 1
- Phenotypic variation can be due to environmental differences
- Phenotypic plasticity is where a single genotype can produce different phenotypes in response to
its environment
- After reading, you should be able to:
o Explain why phenotypic variation is important for evolution and adaptation
o Describe the factors that influence the expression of phenotypic traits
o Define “phenotypic plasticity” and explain how it relates to evolution
o Identify the main components of, and be able to efficiently use, a compound and stereo
o Use an ocular micrometer to calibrate a compound and stereo microscope
o Understand how to design an experiment to test a hypothesis
Background Information
- Phenotype is outward appearance or observable manifestation of a specific genotype
- When Darwin first assembled theory of evolution by natural selection, he implied a struggle for
survival, so the winners are those whose phenotypes afford them the greatest fitness in a given
- Organism’s overall phenotype composed of its morphology, behavior, and physiology when
variation in phenotype is observed within a population ,observed variation may result from
variation among genotypes, environment, or interactions of these two components
- Evolution in populations depends on phenotypic traits being passed down from generation to
generation organism’s alleles and not its phenotype that are transmitted directly from parents
to offspring
- Genotype is complete genetic constitution of an organism
- Genes contain blueprints of phenotypic traits phenotypic trait may arise from expression of
single gene or multiple genes
- Continuous phenotypic traits such as height or skin colour are result of interactions between
multiple genes and often the environment each gene can have a large or small effect on
phenotypic expression
- Traits are referred to as quantitative or polygenic traits
- Individual’s phenotype may not solely rely on its genotype; may depend on environment, or on
interaction between environment and genotype
- Both gene expression and fitness are dependent on environment, individual’s ability to respond to
environmental conditions in a way that will increase its fitness is an important factor in evolution
- Individual’s that can exploit appropriate combination of phenotype and environment will gain
highest fitness can be achieved by altering environment or altering phenotype
- Alteration of phenotype, acclimation, occurs in individuals that are able to modify phenotype in
response to environmental variation in a manner that improves fitness
- Individuals don’t adapt, they acclimate to their environment; populations adapt to changing
- When individual can alter expression of a phenotypic trait in response to environment, they are
showing phenotypic plasticity for that trait concept used to describe degree to which a given
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genotype can alter its phenotypic expression in order to acclimate to its surroundings; ability of
one genotype to produce different phenotypes in different environments
- Phenotypic plasticity expresses itself as discrete alternate types or in a continuum
- When phenotypic plasticity expresses itself in a continuum, relationship between environment
and trait in question is known as a reaction norm
- Potential for an organism to produce a range of different, relatively fit phenotypes in multiple
environments appears to be a successful evolutionar innovation
- Insufficient genetic variation exists for evolution of plasticity to occur is why its not possible for
all traits to be phenotypically plastic; another explanation could be that there are inherent costs
and limitations to the benefits that phenotypic plasticity may provide
- Even if sufficient variation exists for evolution of plasticity, costs and limitations may result in a
selective pressure against a trait evolving phenotypic plasticity
- Costs associated with producing new phenotypes and maintaining sensory and regulatory
mechanisms required for plasticity may offer significant selection pressure against evolution of
plasticity for a trait
- At genetic level, linkage between genes might produce a situation whereby genes promoting
plasticity might be linked to genes conferring a low fitness for other traits
- Limitation associated with producing new phenotypes is accuracy with which an organism can
correctly process environmental cues in order to appropriately acclimate incorrectly sensing
environment, or if environment changes rapidly, organism may produce a maladapted phenotype
- Time difference between sensing environmental change and alteration of phenotype is another
limitation during this time, organism will experience reduced fitness since its not acclimated
yet to its new environmental conditions; greater change in phenotype, longer the time lag
- If all individuals within a population have same expression for a phenotypic trait, trait will
presumably have same effect for whole population on an individual’s chances of surviving or
reproducing in their environment
- If individuals within population vary in expression of a phenotypic trait, they may vary in chances
of surviving and reproducing
- If variation in trait is heritable, then trait will be passed on to next generation
- In phenotypically plastic traits, observed phenotypic variation itself is not heritable because
different phenotypes are produced by same genotype
- Ability for trait to be plastic is a heritable trait
- Heterogeneous environments can lead to selection for plasticity of a trait because they can change
frequently over space and time individual that can produce more than one phenotype is more
likely to acclimate to changing conditions than an individual who can express only one phenotype
Part A: Phenotypic Variation in Phymata Americana
- Natural history of phymata Americana
o An ambush bug found in eastern Canada and S
o Ambush bug clade diverged from rest of assassin bugs approximately 114 million years
ago in neotropics
o Peak activity and mating period of jagged ambush bugs is late summer; females spend
most of time sitting and waiting for prey, while males actively seek out females
o When male finds a potential mate he couples with her, standing on her back and guarding
her from potential rivals
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