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Chapter 17
Population Genetics and Speciation
• Population genetics – the study of the
frequency and interaction of alleles and
genes in populations.
*Microevolution can be studied by observing
changes in the numbers and types of alleles
in populations.
• Normal distribution – a line graph
showing the general trends in a set of data
of which most values are near the mean.
– *Biologists study polygenic phenotypes by
measuring each individual in the population and
then analyzing the distribution of the
measurements.
• **Genetic variation and change are
measured in terms of the frequency of
alleles in the gene pool of a population.
• ***The major source of new alleles in a
natural population is mutation in germ cells.
(The sperm and ova)
• Genetic equilibrium – a state in which the
allele frequencies of a population remain in
the same ratios from one generation to the
next.
Forces of genetic change:
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Gene flow
Nonrandom mating
Genetic drift
Mutation
Natural selection
• *Sexual reproduction creates the possibility
that mating pattern or behaviors can
influence the gene pool of a population.
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**Allele frequencies are more likely to
remain stable in large populations than in
small populations.
Forming New Species
** Speciation has occurred when the net
effects of evolutionary forces result in a
population that has unique features and is
reproductively isolated.
• Reproductive isolation – a state in which a
population can no longer interbreed with
other populations to produce future
generations.
• Subspecies – a taxonomic classification
below the level of species; refers to
populations that differ from, but can
interbreed with, other populations of the
same species.
Mechanisms of Isolation
• Geography
– A physical barrier
• Ecological Niche
– Role the species has in the environment
• Mating Behavior and Timing
– Patterns, sounds, actions, etc.
• Polyploidy
– Cannot pair gametes due to having an extra pair.
• Hybridization
– When two closely related species have offspring.
– Often times the offspring are sterile
– Example = mule (offspring of a donkey and
horse)
Extinction
• Occurs when a species fails to produce any
more descendents.
****The species that exist at any time are the
net result of both speciation and extinction.
-if you think of speciation as like a branch
off of a family tree, then extinction is like
the loss of one of those branches.
Assignment
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Pg. 417: 7-11
Pg 418: 19-20
Pg. 419: 1-9
Due on Monday