Chapter 25 - Iowa State University

Chap 24:
Population Genetics
Supplemental Instruction
Iowa State University
Biology 211
Dr. Holscher
The Hardy-Weinberg equation: p2 + 2pq+q2=1
p^2 & q^2 represents: the frequencies of the homozygous genotype
2pq represents: the frequency of the heterozygous genotype
Question: Using the Hardy-Weinberg equation solve the following questions. What is the allele frequency of a
population that is 74% homozygous dominant? What percent of the population is heterozygous
P2 is .74 take the square root= .86=p
1. Changes in allele frequency due to random chance describes what? Genetic drift
2. Describe bottleneck effect and founder effect
i. (Bottleneck effect)
-A sudden change in the environment may
drastically reduce the size of the population
ii. Founder effect)
-Occurs when a few individuals become
isolated from a larger population, this new group establish a new
population whose gene pool differs from the source population
3. How does migration alter allele frequency between two different established populations?
Decrease between pop, increase within pop
4. True or False: The smallest unit that can evolve is a population and thus is also the smallest unit that can be
selected for by natural selection? False individuals selected for
5. Natural selection is different than all other agents of microevolution that change the gene pool because natural
selection is…
6. What are the three types of natural selection? Draw a curve that would represent each type.
Directional: ind, at one extreme has more offspring
Stabilizing: middle have more
Diversifying/ disruptive: individual at both end have more offspring
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7. Which of the above types of natural selection can lead to speciation? Diversifying
8. Causes of Speciation:
Reproductive Isolation: impedes two subspecies from producing fertile offspring
Prezygotic isolating mechanisms: (impede members of different species from mating)
Before fetili
What are the 5 types of prezygotic isolating mechanism called? Describe each.
i. Habitat isolation
ii. Temporal Isolation
iii. Behavioral Isolation
iv. Mechanical Isolation
v. gametic isolation: gametes of diff. species raraly fuse to form zygote
Postzygotic isolating mechanism: (prevent the interspecies hybrid zygote from developing into a viable,
fertile offspring)
After fertil
What are the 3 types of postzygotic isolating mechanism called?
i. (Hybrid sterility)
ii. (Hybrid inviability)
iii. (hybrid breakdown)
Mechanism of Speciation
1. Allopatric speciation:
a. Occurs when some members of a species occupy a habitat……………………..
from other members
Regions in which members of different species meet and mate, producing some offspring
of mixed alleles is called? (hybrid zone)
3. Sympatric speciation
a. Occurs in populations that live in _______ geographic area. (same)
Patterns of Speciation:
1. Cladogenesis (Branching): Budding of one or more new species from a parent species
that continues to exist.
Anagenesis: Transformation of an unbranched lineage to a new species different
from ancestral population
???? which mechansism of speciation would be the most common cause of