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natural selection and genetics that took shape by the 1940s and is generally accepted today. In summary, the
modern synthesis describes how evolutionary pressures such as natural selection can affect a population's
genetic makeup, resulting in the gradual evolution of populations and species. The theory also connects this
gradual change of a population over time, called
microevolution
, with the processes that gave rise to new
species and higher taxonomic groups with widely divergent characters, called
macroevolution
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4.2 Reading Resource #3:
Mechanisms of Evolution
The Hardy-Weinberg equilibrium principle says that frequencies in a population
will remain constant
in the absence of the four factors that could change them. Those factors are
natural selection
,
mutation
,
genetic
drift
, and
migration
(gene flow). In fact, we know they are probably always affecting populations.
Natural Selection
Natural selection has already been discussed. s are expressed in a phenotype.
Depending on the
environmental
conditions, the phenotype confers an advantage or disadvantage
to the individual with the
phenotype relative to the other phenotypes in the population. If it is an advantage, then that individual will
likely have more offspring than individuals with the other phenotypes, and this will mean that the behind the
phenotype will have greater representation in the next generation.
If conditions remain the same, those
offspring, which are carrying the same , will also benefit. Over time, the will increase in frequency in the
population.
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