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Evolution: Microevolution. Chapter 16. Microevolution evolutionary changes below species level refers to change within a species changes in gene frequency due to natural selection driving force of evol . Population Genetics study of microevolutionary change - PowerPoint PPT Presentation
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Evolution:Microevolution
Chapter 16
I. MicroevolutionA. evolutionary changes below species level
• refers to change within a speciesB. changes in gene frequency due to natural selectionC. driving force of evol.
II. Population Genetics A. study of microevolutionary changeB. evol. takes place as changes occur in a gene pool
• all of the genes present within a pop.C. gene frequencies change as organisms adapt to a
changing env.1. alleles for more adaptive phenotypes increase in freq.2. alleles for less adaptive phenotypes decrease in freq.
D. if gene frequencies change, then evolution occurs
III.Hardy-Weinberg (HW) PrincipleA. math. model used to predict behavior of allele freq. in
an ideal pop.B. allele freq. remain constant from generation to
generation, unless outside forces change them 1. HW equilibrium2. changes occur through natural selection and other
meansC. p2 + 2pq + q2 = 1D. if a population is not in HW equilibrium, then evol. is
occurring• gene freq. are changing
IV. Outcomes of Natural SelectionA. most traits within a pop. form a normal distributionB. stabilizing selection
1. intermediate (avg.) phenotype is most adaptive and selected for
2. alleles for average individuals increase in number
Stabilizing selection
Fig. 16.9 Human birth weight, an example of stabilizing selection
C. directional selection1. one extreme phenotype is most adaptive and
selected for
2. a new “average” is established
Directional selection
Fig. 16.10 An example of directional selection. Guppies become more colorful (blue and yellow lines on graph) in the absence of predation, and less colorful (red graph line) when in the presence of predation.
D. disruptive selection1. both extreme phenotypes are adaptive and
selected for2. two “averages” are formed
Disruptive selection
Fig. 16.8 Three different kinds of selection: (a) stabilizing, (b) directional, and (c) disruptive
Another real example of the three different kinds of selection
V. Other Ways Evolution Can Occur in Addition to Natural SelectionA. genetic drift
1. change in allele freq. due simply to random chance
2. more pronounced effect in small populations
3. can lead to the complete loss or fixation of certain alleles in a pop.
An example of genetic drift
Fig. 16.6 Genetic drift
B. population bottleneck1. pop. is greatly reduced in a small amount of time
• usually due to a natural disaster or major disease of some kind
2. gene freq. change according to those possessed by the survivors
Schematic view of a population bottleneck
C. founder effect1. small group of individuals
leave main pop. and establish a new colony
2. gene freq. change according to those possessed by these “founders”
D. gene flow• exchange of genes between
pops. of the same species
Schematic view of founder effect