Leader: Kirsten Karkow
Course: Biol 211 - Wilsey
Date: 3/28/2012
Worksheet 23
Supplemental Instruction
Iowa State University
What are the five assumptions of the Hardy-Weinberg Equilibrium model?
1.
2.
3.
4.
5.
Very large population size (N)
No mutation
No migration
Completely random mating
No natural selection
Define the following terms:
Carrier – individuals with the heterozygote genotype (not just any individual carrying a diseased
allele, i.e. not persons homozygous for that disease). THEY CARRY THE DISEASE (don’t express).
Mutation – heritable change in DNA. Can be beneficial, harmful, or neither.
Genetic Drift – random change in the allele frequencies of a population. Especially pronounced
in SMALL populations.
Bottleneck Effect – occurs when large chunk of population dies off. Only a small population
survives, so is subject to pronounced genetic drift due to limited gene pool.
Founder Effect – occurs when a small population travels to some isolated, previously
uninhabited (by that species) territory. Again, subject to pronounced genetic drift.
Gene Flow – migration, movement of individuals from one population to another.
Sexual Selection – refers to preferential mating due to “attractiveness” in some form.
Directional Selection – occurs when an individual at one extreme has greatest fitness.
Diversifying (Disruptive) Selection – occurs when the two extremes have greatest fitness. This
can lead to speciation (over time the two extremes can no longer interbreed).
Stabilizing Selection – occurs when the intermediate individual has greatest fitness.
Fill in the blanks:
Natural selection acts on individuals. Evolution occurs in populations.
Evolution occurs when there are changes in allele frequencies (microevolution) in genes that
are phenotypically expressed. If the different alleles don’t result in some sort of definitive
phenotype, natural selection can’t act on them.
Of all the processes leading to microevolution, only natural selection is adaptive (matches the
individual to the environment.) The rest are random.
Supplemental Instruction
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