Genetic Variation & Evolution1 Genetic variation and Evolution Chapter 20 Why are organisms well adapted to their habitats? Creationist explanation (see section 21.7) Is a religious view Divine role “intelligent design” not scientifically testable Scientific explanation “evolution from common ancestor” ‘Natural Selection” -- is testable Question Read or listen to the The Firing Line 1997 Creation-Evolution Debate should know H-W equation and why it’s important -- we may come back to this 20.4 – understand the meaning of fitness, but we’ll not cover the mathematical aspects 20.5 – skip 20.6 – read on your own 20.8 – read on your own

Genetic Variation & Evolution2 Lamarck’s theory of “Inheritance of Acquired Traits” Question Darwin was not first to describe evolution George Cuvier (1790) – Fossils & ‘Catastrophism’ Jean Lamarck (1809) -- Environmental influence

Genetic Variation & Evolution3 Modern explanations of why traits change over time (20.3) -- Frequency of genes in the population change 5 Agents (mechanisms) of change: 1. Genetic Mutation – random changes to DNA code -- creates variation in traits -- ‘raw material’ of all evolutionary mechanisms 2. Natural selection – mechanism proposed by Darwin -- environment selects certain traits

Genetic Variation & Evolution4 Agents of change, con’t Other agents of change 3. Gene flow -- movement of individuals between populations 4. Nonrandom mating -- organisms prefer to mate with certain individuals 5. Genetic drift -- chance may favor certain traits in a small population Founder effect – population isolation bottleneck effect – population catastrophe -- gene pool reduction Founder effectBottleneck effect Gene Flow

Genetic Variation & Evolution5 What are the fundamental premises of Darwin’s theory of “Natural Selection”? Read Section about Evolution in Chapter 1 “On the Origin of Species by Means of Natural Selection” “Evolution” (a process) does not equal “Natural Selection” (a process) Natural selection occurs when: 1) There exists genetically based variation (inheritable) in the traits of a species. 2) Organisms produce more offspring than can survive. 3) The environment selects for those organisms with the best adapted traits. 4) Organisms best adapted to the environment will reproduce most successfully.

Genetic Variation & Evolution6 How does Darwin’s ‘Natural Selection’ explain giraffe evolution? “Selective Pressures” “Adaptation” -- a noun and verb -- not an ecological term

Genetic Variation & Evolution7 What is nature of genetic variation? (20.1) Genetic mutation DNA Polymorphisms Different ‘alleles’ Hardy-Weinberg equation (20.2) p 2 + 2pq + q 2 -- frequency of Alleles  frequency of traits -- can provide evidence for selection Genetic variation in Asiatic lady beetle Question

Genetic Variation & Evolution8 What are examples of environmental selective pressures? Predator-prey interactions Competition for resources Human impacts Natural selection acts upon existing genetic variation -- theory is not ‘teleological” Wrong: “In order to hide from predators, the dead-leaf butterfly evolved a leaf-like appearance.” Better: “Predation selected for butterflies that most resembled a dead leaf.” The environment selects among but does not create variations! Question

Genetic Variation & Evolution9 Do organisms always produce more offspring than can survive? Cichlides: Carmagnola Grey rabbit:Humans: 250,000 eggs 5-8 litters x 7 offspring 2- 7 children/family

Genetic Variation & Evolution10 Why don’t humans evolve wings? Limits of Selection Existence genetic variation Complex traits involve many genes Suitable selective pressures Genes have multiple effects -- developmental genes Question

Genetic Variation & Evolution11 What is ‘Artificial Selection’? All these crops are varieties of the species Brassica napa Colors represent different genetic types. Map shows genetic variation in Africa. Group project Are humans still evolving?

Genetic Variation & Evolution12 Why does ‘in breeding’ cause genetic problems? species non-inbred inbred Zebralived203 died 72 Eld’s deerlived130 died 47 Giraffelived112 died 33 Oryxlived350 died 25 Dorcas lived3617 gazelledied1425 From Klug & Cumminings Genetics 5 th ed

Genetic Variation & Evolution13 What are the effects of Natural Selection on a population? (20.7) “Microevolution” vs “Macorevolution”

Genetic Variation & Evolution14 What is the effect of Directional Selection on a population? Progressive change in a trait within a species

Genetic Variation & Evolution15 How does Stabilizing Selection affect a population? Human birth weight & Eurosta gall size Stabilizing selection & ‘living fossils’

Genetic Variation & Evolution16 How does Disruptive Selection affect a population? Responsible for divergence of a single species into two different species Modern example of process: blackbellied seedcracker Question