This document discusses gene pools, speciation, and mechanisms of reproductive isolation. It defines key terms such as allele frequency, gene pool, and types of reproductive isolation like geographical, temporal, and behavioral isolation. Mechanisms of speciation discussed include gradual divergence of isolated populations and abrupt speciation. Examples of natural selection pressures like directional, stabilizing, and disruptive selection are provided, as well as speciation through polyploidy in plants. The document contrasts theories of gradualism and punctuated equilibrium in the rate of speciation. Homework questions are assigned related to defining terms and challenging concepts.

1. 10.3: Gene Pools and Speciation

2. Guidance
Punctuated equilibrium implies long periods without appreciable
change and short periods of rapid evolution.
Understandings
Applications/Skills
 A gene pool contains all of the genes and their different alleles
present in an interbreeding population.
 Evolution requires that allele frequencies change with time in
populations.
 Reproductive isolation of populations can be temporal,
behavioral, or geographic.
 Speciation due to divergence of isolated populations can be
gradual.
 Speciation can occur abruptly.
 A: Identifying examples of directional, stabilizing, or
disruptive selection.
 A: Speciation in the genus Allium by polyploidy.
 S: Comparison of allele frequencies of geographically
isolated populations.

3. Allelic Frequency
 A measure of the
proportion of a
specific variation of
a gene in a
population.
 Does not indicate
the number of
individuals with that
allele.

4. Reproductive Isolation
 Geographical- a physical barrier is preventing
males and females from breeding.

5. Reproductive Isolation
 Temporal isolation-
incompatible
timeframes

6. Reproductive Isolation
 Behavioral isolation- lifestyles/habits are not
compatible.
 Ex: Eastern/Western meadowlark

7. Directional Selection
 When one phenotype is favored as a result of
natural selection.
 Frequency of the favored phenotype increases
and frequency of the other decreases.
 Ex: peppered moth

8. Stabilizing Selection
 When an intermediate phenotype is favored over
two extremes.

9. Disruptive Selection
 When two extreme phenotypes are favored over
an intermediate.

10. Polyploidy
 A cell contains 3 or more
sets of chromosomes (3n,
4n, etc)
 Can happen during cell
division- both sets of
chromosomes go to one
cell.
 Can lead to different rates
of evolution between
populations of the same
species.
 Over time, may lead to
speciation; plants no
longer able to interbreed.

11. Gradualism
 Speciation occurs at a steady rate
with small changes over long
periods of time (Darwin).

12. Punctuated Equilibrium
 Speciation happens quickly as a result of change
in the environment (like a natural disaster).
 Some species are destroyed and others adapt.
 Reduction in competition

13. Homework
 Define the following
Gene pool
Population Triploid, Tetraploid,
Inbreeding Pentaploid
Interbreeding Gradualism
Allele frequency Punctuated Equilibrium
Reproductive isolation Directional Selection
geographical Stabilizing
Selection
temporal Disruptive Selection
behavioral

14. More homework!
 Pg 444- Challenge yourself 5 and 6
 Pg 445- Summarize Nature of Science
 Pg 448- Exercises 7-9, TOK