Biology 101: Spring 2007
How organisms evolve (Part 2)
Lecture outline
I.
What causes evolution? [Text, 15.2]
1.
Mutation (previous lecture)
2.
Gene flow (previous lecture)
3.
Small population size

Genetic drift (general example)

Population bottleneck

Founder effect
4.
Non-random mating (assortative mating)
5.
Natural selection [Text. 15.3]

Review of key principles

Compromise based on differing selective pressures

Types of selective pressures (including examples)

Three ways that natural selection affects populations (i.e. directional
selection, disruptive and stabilizing selection)
Study questions
1.
In general, which is more impacted by random events, the allele frequencies of a small
population or of a large population? What is this change in allele frequencies due to
random events called?
2.
Northern elephant seals were used as an example of a population bottleneck.
a.
What was the bottleneck event, and how, specifically did it impact the population?
b.
What were the consequences of this bottleneck in terms of the population’s
numbers and variability?
c.
What characteristic of elephant seal mating systems might have made the condition
you describe in “b” more extreme?
3.
Must a population bottleneck reduce diversity? (In other words, would it be possible to
have a population bottleneck without a decrease in genetic variability?) Justify your
answer.
4.
Provide an example of the “founder effect.” Explain how the “founder effect” could cause
evolution of a new population (in comparison to the population from which it came),
being sure to incorporate an accurate definition of evolution (as provided in the lecture
and text) into your answer.
5.
What is assortative mating? Provide an example.
6.
Do selective forces act directly on phenotype or on genotype? As a result of selective
forces, which individuals will leave the most offspring? Will the same individuals always
be the most fit in all types of environments? Explain…
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7.
Given that selective forces act directly on phenotype (ooh, gave away one part of the
previous question!), how is it that natural selection leads to evolution, described as
changes in allele frequencies, over generations? (In other words, how can natural
selection act on phenotypes, but select for genes?)
8.
Explain what is meant by “Natural selection acts on individuals, but causes evolution of
populations over generations.” (Emphasize underlined words in your explanation.)
9.
List several types of selective pressures, and provide at least one example of each. Also,
be sure you are familiar with examples introduced in the lecture.
10.
Define “sexual selection.” Are characteristics selected for due to sexual selection always
those that promote survival? Explain. (HINT: See guppy example at end of Chapter 14.)
11.
Describe the three ways that natural selection can affect a population over time, and
include an example of each.
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