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 (Hardy-Weinberg Conditions)  Infinitely Large  Random Mating  Equal Survival  Isolation  No mutations Help Evolution (Natural Conditions)  Small  Genetic Drift Genetic DriftGenetic Drift  Natural Selection  Gene Flow Gene Flow Gene Flow  Mutations POPULATION SIZE MATINGVIABILITY INTERACTION W/ OTHER POPS DNA CHANGES

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 Catastrophe cuts pop size  Decreased variety of traits  Altered genetic makeup  Genetic drift more likely  Founder Effect Small group emigrates to new habitat 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 Environment is stable Initially adaptive form becoming more numerous from many generations of natural selection Initially adaptive form becoming more numerous from many generations of natural selection RANGE OF PHENOTYPES MOST ADAPTIVE FORM

Modes of Selection  Directional Environment is changing (or has changed) Environment is changing (or has changed) Formerly adaptive form is no longer adaptive Formerly adaptive form is no longer adaptive Pop evolves toward newly adaptive form Pop evolves toward newly adaptive form MOST ADAPTIVE FORM RANGE OF PHENOTYPES

Modes of Selection  Disruptive (Diversifying) Intermediate form is undesirable and decreases in # Intermediate form is undesirable and decreases in # 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. Do not add any materials. Put your names on the ctuki. Put your names on the ctuki. Your ctuki must be able to asexually reproduce in class (it should take no more than one minute). Your ctuki must be able to asexually reproduce in class (it should take no more than one minute).