DO NOW: What comes to mind when you hear the word “EVOLUTION” HOMEWORK: Complete the “In your Own Words” Section of the Hummingbird Activity.

Genetic changes in a population or species over time EVOLUTION: Genetic changes in a population or species over time

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

Macro-Evolution Micro-evolution leads to Macro-evolution Large-scale, often over a very long time Branching of one species into two species Leads to the idea that all species share a common ancestor Example: Evolution of whales from four-legged land mammals Micro-evolution leads to Macro-evolution

Some New Evolution Terms Population Group of individuals from the same species that interbreed Gene Pool All the genes and all of their alleles in population Relative Frequency The proportion of one allele in the whole gene pool Evolution (on a population scale) Any change in the relative frequency of alleles over time One allele becomes more common, another becomes less common Change in a population NOT change in an individual Fitness The ability of a particular genotype to reproduce and pass on its genes to the next generation

Hummingbirds and Evolution How does evolution really work? Let’s look at the scientists studying natural selection in Hummingbird Populations in Ecuador: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html

Selection – differential survival and reproduction of individuals with different genotypes Natural selection involves… More offspring are born than can survive Competition/struggle for survival for limited resources Variation between individuals that makes some better able to survive and reproduce This variation is heritable/genetic (can be passed on) Result: Over many generations, the genotypes that are better able to survive and reproduce become more common in the population.

Sources of Genetic Variation Mutations Any change to a DNA sequence Rare Sometimes harmful, sometimes helpful Mutations to egg or sperm = inheritable Mutations to body cells = not inheritable (CANCER) Gene Shuffling Meiosis divides the genetic info and fertilization recombines it 23 pairs of chromosomes = 8.4 million different combinations of genes Crossing Over during meiosis increases the number of different combinations of alleles

Galapagos Finch Activity…

Let’s think back: What are the connections to Sickle Cell Anemia and Natural Selection? Recessive Disorder Result of a single gene mutation in hemoglobin, the substance that helps blood cells carry oxygen. Amino acid valine replaces glutamic acid in the hemoglobin protein, making blood cells sickle-shaped. People who are heterozygous are partially resistant to malaria (carried by mosquitoes)

Balanced Polymorphism (a. k. a Balanced Polymorphism (a.k.a.: Heterozygote Advantage) Ex: sickle cell anemia

DO NOW: What is the difference between polygenic vs. single gene traits? HOMEWORK: no homework… unless you feel like revising the Galapagos Finch Activity (note: 5% reduction)

Human Inheritance Single Gene Traits: Polygenic Traits: Traits controlled by a single gene (A or a) i.e.: widows peak Polygenic Traits: Traits controlled by two or more genes Often with more than two alleles for gene. i.e.: skin color, eye color, body shape, height, etc.

Frequencies of Polygenic Traits

3 Modes of Selection for Polygenic Traits: Directional Selection Stabilizing Selection Disruptive Selection Remember: Natural Selection only really acts on the organism NOT the genes. It only selects for traits based on whether the organism dies or lives to reproduce.

Directional Selection Individuals with Phenotypes at one extreme die off or fail to reproduce Individuals with Phenotypes at the other end have greater fitness and leave a higher number of offspring. This shifts the relative frequency in the direction of the successful extreme. When it Happens: If there is a change in the environment that favors the phenotype at one extreme and not the other. http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html

Stabilizing Selection Individuals with phenotypes at both extremes die off or fail to reproduce. Individuals with intermediate phenotypes have better survival. Results in populations of individuals with intermediate phenotypes. Less variation at the extremes. http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html

Disruptive Selection Individuals with phenotypes at both extremes have better survival Individuals with intermediate phenotypes die off or fail to reproduce Can result in two distinct phenotypes, which can lead to subpopulations http://www.gwu.edu/~darwin/BiSc150/PopGen/NS.html

What kind of selection is this?

Galapagos Finches

DO NOW: Log Into Your Computers! Tuesday: 4.28.09 DO NOW: Log Into Your Computers! HOMEWORK: Read Section 16-3 (pgs. 404 – 410) Finish Analyzing Data Questions (pg. 408 #1-4) On page 410, answer questions #1-3.

Key Questions: 1. What is the evidence that one species can branch into two? 2. What is the evidence that multiple species are evolutionarily related?

Evolution Dry Lab Part A: Computer Lab: All in the Family: Which Animals are the Closest Relatives? Link: http://www.pbs.org/wgbh/evolution/change/family/index.html

DO NOW: What do you think a “species” is? Wednesday: 4.30.09 Title: Species and Speciation DO NOW: What do you think a “species” is? HOMEWORK: No HOMEWORK TONIGHT (unless you need to work on Part A or revise last night’s HW) 

SPECIES A group of similar organisms Breed with each other Produce Viable Offspring

Speciation – The formation of new species. The gene pools of two populations must become separated Ex: The Galapogos Finches

Steps of Speciation: Reproductive Isolation Changes in the Gene Pool Gene Pools Diverge Genetic Barriers to Reproduction

I. Reproductive Isolation One population becomes isolated from 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 Conditions of their local environment select certain traits Temporal Species reproduce at different times or have other behavior that becomes time sensitive (i.e.: feeding)

II. Changes in the Gene Pool Gene Pools Diverge: The isolated populations become genetically different. Due to selection and/or genetic drift Two separate gene pools emerge Genetic Barriers to Reproduction The two populations are no longer able to interbreed Due to genetic differences in habitat preference, mating behavior, or physical compatibility Competition may arise between these two new species They are now 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 After mating occurs Hybrid inviability Hybrid breakdown Hybrid sterility

Famous Hybrids

(Less so)… Famous Hybrids Real-World Research…

Move to “Evidence for Evolution Presentation”