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STAT 2230 (44)
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Lecture

# Chapter 9.doc.docx

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School
Department
Statistics
Course
STAT 2230
Professor
Dan Meegan
Semester
Fall

Description
What Evolutionary Mechanisms Result in Adaptation?  Adaptation occurs when some individuals in a population contribute more offspring to the next generation that others allele frequencies in the population change in a way that adapts individuals to the environment that influenced such reproductive success (natural selection).  Natural selection acts on the phenotype.  The reproductive contribution of a phenotype to subsequent generations relative to the contributions of other phenotypes is called its fitness.  Changes in absolute numbers of offspring are responsible for increases and decreases in the size of a population, but only changes in the relative success of different phenotypes within a population lead to changes in allele frequencies from one generation to another.  The fitness of a phenotype is determined by the average rates of survival and reproduction of individuals with that phenotype. Natural selection produces variable results  Natural selection can act on characters with quantitative variation in any one several different ways: o Stabilizing selection—favouring average individuals o Directional selection –favouring individuals that vary in one direction from the mean pop. o Disruptive selection—favouring individuals that vary in opposite directions from the mean of the population. Sexual selection influences reproductive success  Sexual selection is a special type of natural selection that acts on characteristics that determine the reproductive success.  Sexual selection may favour traits that enhance the bearer’s chances of reproduction, but reduce its chances of survival. o Such costly traits reliably demonstrate the quality of their possessors as mates b/c they enable the choosing sex (usually females) to distinguish between genuinely fit individuals and exaggerators. How is Genetic Variation Maintained within Populations? Neutral mutations may accumulate within populations  An allele that does not affect the fitness of an organism is called a neutral allele.  Neutral alleles are unaffected by natural selection.  Neutral alleles tend to accumulate in a population over time, providing it with con
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