Population Genetics: Evolution at the Gene Level

1. Fossils show change over time
 scientists can ___________________ & use them to support the
 ________________________________________________________
Anatomy of living species also shows relatedness
Homologous Structures
 _____________________________ because they share a common ancestor:
 Ex: human arm, dog front limb, horse leg, whale
3. Analogous structures
Distantly related species have _______________________________ but are ________________ in
structure _________________________
 Ex: wing of butterfly & bird
4. Vestigial structures
Structures ________________ & often ____________________
 ___________________ of functional structures
 Ex: leg & hip bones in pythons & whales
5. Molecular Evidence
 Also called ______________________ evidence
 Compares ____________________ (ex DNA, amino acid sequences) between organisms
 Related organisms have more of the same molecules in common
How do new species form?
1. Geographic Isolation
 When members of a population are separated
 Ex: polar, grizzly, & black bears
2. Reproductive Isolation
 When members of a population can’t breed even though they live nearby
 Ex: different mating seasons or different mating calls
4 Different Types of Evolution
1. Divergent Evolution
-___________________ populations evolve ______________________
Ex: polar & grizzly bears changed independently due to different habitats
2. Convergent Evolution
-Unrelated species become _________________ because they live in ___________________
Ex: shark & dolphin
3. Coevolution
- Species that _____________________ adapt to ________________
Ex: flowers & hummingbirds
4. Adaptive Radiation
- Evolution of ____________________________ from _________________common ancestor
Ex: ________________________________________
Population Genetics: Evolution at the Gene Level
Natural Selection:
4 Steps of Natural Selection:
Allele Frequency:
If 100 individuals make up a population and 50 are homozygous dominant, 25 are heterozygous,
and 25 are recessive, what is the allele frequency of the dominant allele?
You try!
If 300 individuals make up a population and 150 are homozygous dominant, 100 are
heterozygous, and the rest are recessive, what is the allele frequency of the recessive trait allele?
How does natural Selection affect allele frequency?
• Mutations provide the raw material on which natural selection can act.
• Evolution depends on ___________ because this is the only way that _____________ among organisms
are created
• Evolution acts on populations not ________________.
Survival of the Fittest:
o If individuals having certain genes are better able to produce mature offspring than those without
them, the frequency (number #) of those genes will increase.
o Survival:
o Fitness:
Different Lines of Evidence:
• Wolf Lineage:
Darwin’s Finches:
Whale DNA:
Genetic Drift:
Example: __________________________________ -- a rare form of dwarfism that includes
extra digits -- in the Amish population of eastern Pennsylvania, which has intermarried over many
Example: ____________________________________was changed when U.S. Soldiers had
children with Vietnamese women during the Vietnam war.
Gene Flow:
Founder Effect:
The population then will contain only those genes the initial individuals brought with them.
• Example:
Bottleneck Effect:
Example: __________________________________________
the population has rebounded from this population bottleneck to some 100,000 animals today.
However, these animals are homozygous at every one of the gene loci that have been examined.
Types of Natural Selection:
Stabilizing Selection:
example is
Directional Selection:
• Individuals at either end of the distribution curve are favored.
• Example:
Diversifying (Disruptive Selection)
• A Cladogram is a _______________________ that depicts species divergence from
They show the ________________distribution and origins of
• Cladograms are _________________________________
phylogenetic relationships.