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 Evolution (on a population scale) 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

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 Micro-evolution leads to Macro-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 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 Reproductive Isolation 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 Behavior: Changes in courtship or other reproductive strategies Geographic 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 Gene Pools Diverge (become different): 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!