Transcript Slide 1
Changes in the genetic makeup of populations Natural Selection 1.Populations tend to overproduce offspring. Natural Selection 2. Genetic variation exists within populations Natural Selection 3. The best adapted organisms survive and reproduce in greater numbers. Natural Selection 4. Subsequent generations contain higher frequencies of adapted orgs. Adaptation Inherited trait Increases chance of survival/reproduction Environment-specific Natural Selection The environment determines success of traits 1.Overproduction 2.Genetic variation 3.Struggle for survival 4.Differential reproduction Natural Selection Hardy-Weinberg Conditions Hypothetical conditions that must exist in a population for no evolution to occur. Population Characteristics Hinder Evolution Help Evolution (Hardy-Weinberg Conditions) (Natural Conditions) POPULATION SIZE Infinitely Large Small Genetic Drift MATING Random Mating Natural Selection Natural Selection VIABILITY Equal Survival Isolation No mutations INTERACTION W/ OTHER POPS Gene Flow DNA CHANGES Mutations Genetic Drift Random fluctuations in genetic makeup Example: 2 red, 2 blue orgs seek shelter 50% survive. All are red Blues eliminated by chance (17%) 4 red, 4 blue head for shelter 50% survive. All are red Blues eliminated by chance (1.4%) Genetic Drift Bottleneck Effect Catastrophe cuts pop size Decreased variety of traits Altered genetic makeup Genetic drift more likely Founder Effect Small group emigrates to new habitat Gene Flow Introduction of new traits through immigration May be beneficial or insignificant New traits altered genetic makeup Modes of Selection Stabilizing Environment is stable Initially adaptive form becoming more numerous from many generations of natural selection MOST ADAPTIVE FORM RANGE OF PHENOTYPES Modes of Selection Directional Environment is changing (or has changed) Formerly adaptive form is no longer adaptive Pop evolves toward newly adaptive form MOST ADAPTIVE FORM RANGE OF PHENOTYPES Modes of Selection Disruptive (Diversifying) Intermediate form is undesirable and decreases in # RANGE OF PHENOTYPES MOST ADAPTIVE FORMS MOST ADAPTIVE FORMS Evolution of the Ctukis Ctukis are creatures from a planet you’ve never heard of. You will construct a ctuki out of a single 8½x11 sheet of paper. Do not add any materials. Put your names on the ctuki. Your ctuki must be able to asexually reproduce in class (it should take no more than one minute).