Biology Reference
In-Depth Information
Selection
Disruptive
or
variable
Directional
or
stabilizing
+
-
Population 2
+
Population 1
Between populations
genetic diversity
Mutation
within population
genetic diversity
+
Migration
Population 3
-
Genetic drift
FIGURE 14.1
Effects of the four main evolutionary forces on within-population genetic diversity: a process leading to conser-
vation or increase + , or to reduction - of the within-population genetic diversity.
to selection; this kind of polymorphism is particularly analyzed in population genetics to
characterize within- and between-population genetic diversity. On the other hand, muta-
tions in coding sectors for a functional protein or for a transcription factor can considera-
bly affect individual physiological performance or organism fitness.
Particular noncoding regions of the genome consist of many copies of the same sequence
(two to nine nucleotides) and are called microsatellites. These markers display a high natu-
ral mutation rate, and thus are particularly targeted in explorations of the genetic structure
of populations in the field and to analyze mutation load in populations.
14.2.2 Genetic Drift
Genetic drift refers to fluctuations in allele frequency that occur by chance, especially in
small populations, as a result of sampling error. In small populations, in particular, genetic
drift effects are frequently relatively dominant to those of selection, high-performance
genotypes and genotypes sensitive to stress displaying the same extinction probability
(Hauser et al. 2003). Genetic drift leads to an increase in the genetic differentiation between
populations.
14.2.3 Migration
Migration is characterized by the movement of individuals between populations, whereas
gene flow is the movement of genes between populations, i.e., is linked to the successful
reproduction of an immigrant in its new habitat. Generally, gene flow leads to an increase
of within-population genetic diversity and to a decrease of between-populations genetic
diversity, i.e., to a lower level of genetic differentiation.
 
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