Download Evolution and Natural Selection Notes

INTRODUCTION TO
EVOLUTION
PHA Biology 9
Moretti/ Dickson
EVOLUTION

Genetic changes in a species or
population over time
Connecting Genetics and Evolution:
Cystic Fibrosis Case Study
Figure 1. Chest Radiograph of
CF Diffuse Interstitial Disease
Image:
http://www.eradimaging.com/site/article.cfm?ID=327:
Reprinted with permission from LearningRadiology.com.
Case of the Week Archives—2003. Cystic Fibrosis.
Available at:
http://www.learningradiology.com/toc/tocsubsection/t
ocarchives2003.htm. Accessed January 28, 2008.11
Agenda & Goals for Today:

Share ideas from the Do Now
How does cystic fibrosis illustrate evolution?
 What causes evolution?


Notes
Vocabulary – Define population, gene pool, and fitness
 Levels of Evolution – Explain the difference between micro and
macro-evolution
 Natural Selection – Identify key principles of natural selection


Videos:
Evolution in Hummingbirds
 Evolution in Bacteria
** Announcement: Optional Challenge Questions **

Vocabulary

Population


Gene Pool


Group of individuals from the same species that live in the same
area and interbreed
All the genes and all of their alleles in a population
Evolution (on a population scale)

Any change in the proportions of alleles over time



(One allele becomes more common, another becomes less common)
Change in a population NOT change in an individual
Fitness

How well a particular organism can survive and reproduce to pass
on its genes to the next generation
Objectives for Class:
• Use actual evidence to explain how the four principles of natural selection shape the evolution of organisms
Macro-Evolution



Large-scale, often over a very long time
Branching of one species into two species
All species share a common ancestor
Example: Evolution of whales from four-legged land
mammals
Objectives for Class:
• Use actual evidence to explain how the four principles of natural selection shape the evolution of organisms
Micro-Evolution



Small-scale
Changes in a population’s gene pool over time
Caused by natural selection and/or genetic drift
Example:
CF allele becomes more common in European
populations because it protects against tuberculosis
Micro-evolution leads to Macro-evolution
Objectives for Class:
• Use actual evidence to explain how the four principles of natural selection shape the evolution of organisms
How Does Natural Selection Happen?
Video: Hummingbirds in Ecuador


What are some adaptations that these hummingbirds have?
As we watch the video: make a list of Principles of Natural Selection
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Objectives for Class:
• Use actual evidence to explain how the four principles of natural selection shape the evolution of organisms
Principles of Natural Selection
 Genetic

variation between individuals
Due to mutation and gene shuffling (sexual reproduction)
 More
offspring are born than can survive
 Competition/struggle for limited resources
 Some individuals are more genetically “fit” than others
– they are better at surviving, reproducing, and passing
on their genes
Result: Over many generations, the “fit” alleles become
more common in the whole population because they
are more helpful for surviving and reproducing.
SUMMARY: SURVIVAL & REPRODUCTION OF THE FITTEST
Examples of Natural Selection:
Ex. 1: Long beaks become more common in a
hummingbird population because long beaks help get
food
Ex. 2: Sickle cell anemia becomes more common in
African populations because SCA protects against
malaria
Ex. 3: CF becomes more common in Europeans because
it protects against tuberculosis
Ex. 4: Some TB bacteria have evolved to resist
antibiotics
Video: Evolution in bacteria
(6 minute video)
Notes: SPECIES and SPECIATION
Species  A group of similar organisms
 Can breed with each other and produce
fertile offspring
Examples:
 Human species (Homo sapiens)
 Horses and donkeys = two separate species
because their offspring (mules) aren’t fertile
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Speciation The formation of new
species from a
common ancestor
 The gene pools of two
populations must
become separated

Ex: The Galapagos Finches
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Two Main Steps of Speciation
1.
Reproductive Isolation
2.
Changes in the Gene Pool


Gene Pools Diverge (become different)
Genetic Barriers to Reproduction
Arise
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Reproductive Isolation
One population becomes separated and stops breeding with
the rest of the species
1.
Behavior:

2.
Geographic


3.
Changes in courtship or other reproductive strategies
Geographic barrier splits population (i.e.: river, mountain,
body of water, etc.)
Populations are separated and cannot interbreed
Temporal

Species reproduce at different times or have other
behavior that becomes time sensitive (i.e.: feeding)
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Changes in the Gene Pool
A.
Gene Pools Diverge (become different):


B.
The isolated populations become genetically different.
The new environments or behaviors favor different
genetic traits (natural selection)
Genetic Barriers to Reproduction Arise


The two populations can no longer interbreed
Due to genetic differences in habitat preference, mating
behavior, or physical compatibility
They are now two separate species!
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Hybrid 

The offspring of a mating between two different
species
If a hybrid can’t have offspring, there are still two
separate species!
Reproductive Barriers That Maintain
Separate Species

Before mating occurs






Geographic barriers
Ecological/habitat differences
Temporal differences
Behavioral/courtship differences
Mechanical differences
Chemical differences
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Reproductive Barriers That Maintain
Separate Species

After mating occurs:



Hybrid dies before birth
Hybrid is weak and sickly
Hybrid is sterile (can’t reproduce)
Objectives for Class:
• Explain the defining characteristics of a species
• Describe the 2 steps of speciation
Famous Hybrids
that are strong but
STERILE!