BIO152H5 Lecture Notes - Lecture 3: Isopoda, Frequency Distribution, Genetic Drift

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16 May 2017
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BIO152
Hadia Saeed
May 16th 2017
Lab 3 Natural Selection Notes
Mechanisms of evolutionary change cause changes in frequency of genes in a population
Genetic drift, mutation and migration (gene flow) cause evolutionary change
Natural Selection is one of the key mechanisms of evolutionary change
o Defined as the differential survival and reproduction of organisms that exhibit
differences in heritable traits
o Organisms that're better adapted to their environment will increase in frequency
relative to those that're less suited to their environment
o As long as there is variation in organism populations, there is differential reproduction
because of selection pressures
o Beneficial heritable traits are passed on to subsequent generations and trait becomes
more common in the population
Darwin proposed the net effect of selection of traits could result in the evolution of new
species
o Ex. finches on the Galapagos island, beaks shapes varied considerably in response to the
seeds that the finches eat
o Variation in the phenotypic state of the finches can be visualized in frequency
distribution
o Frequency distribution graphical representation of how many times something occurs
within a group of categories or ranges
o Examples: sorting a random sample of birds and counting according to beak morphology
Then plotting data on a graph with variable on x-axis and frequency on y-axis
This provides the range of phenotypic states and the frequency of individuals
with each phenotypic state
Also provides the mean within the population according to shape of curve and
the amount of variation
Isopods small crustaceans that have 7 pairs of legs and breathe with gill-like structures in the
posterior end of their body
o Because they require gills to breathe they must inhabit wet or moist environments like
marine or moist terrestrial ecosystems
o They are omnivores and scavengers feed on dead and decaying plants and animals
o Predators vary and include; ants, spiders, toads, frogs, some birds, beetles, and even
other isopods
o Vary in size, speed, coloration, and ability to roll into a ball
o Some characteristics are adaptations to elude predators
Overall importance of natural selection seen in potential to produce new species
Earth is diverse in number of species as well as array of genes within these species and varied
environments and ecosystems
Current investigations in evolutionary biodiversity are ongoing and trying to determine how
evolution occurs
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