Introduction to Evolution

INTRODUCTION TO EVOLUTIONPHA Biology 9Moretti/ Dickson

EVOLUTION Genetic changes in a

species or population over time

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/tocarchives2003.htm. Accessed January 28, 2008.11

Connecting Genetics and Evolution:Cystic Fibrosis Case Study

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

Group of individuals from the same species that live in the same area and interbreed

Gene Pool 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

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

Macro-Evolution

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 Selectionhttp://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 SPECIATIONSpecies - A group of similar organisms Can breed with each other and

produce fertile offspringExamples: 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 AriseObjectives for Class:• Explain the defining characteristics of a species• Describe the 2 steps of speciation

Reproductive IsolationOne population becomes separated and stops

breeding with the rest of the species1. Behavior:

Changes in courtship or other reproductive strategies

2. Geographic Geographic barrier splits population (i.e.:

river, mountain, body of water, etc.) Populations are separated and cannot

interbreed3. 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 PoolA. Gene Pools Diverge (become different):

The isolated populations become genetically different. The new environments or behaviors favor different

genetic traits (natural selection)

B. 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!