Changes in the genetic makeup of populations

Natural Selection1.Populations

tend to overproduce offspring.

Natural Selection

2. Genetic variation exists within populations

Natural Selection3. The best adapted organisms survive and reproduce in

greater numbers.

Natural Selection4. Subsequent generations

contain higher frequencies of adapted orgs.

Adaptation Inherited trait

Increases chance of survival/reproduction

Environment-specific

Natural SelectionThe environment determines success of traits

1.Overproduction2.Genetic variation3.Struggle for survival4.Differential reproduction

Natural Selection

Hardy-Weinberg Conditions

Hypothetical conditions that must exist in a population for no evolution to

occur.

Population CharacteristicsHinder Evolution(Hardy-Weinberg Conditions)

Infinitely Large

Random Mating

Equal Survival

Isolation

No mutations

Help Evolution(Natural Conditions)

Small Genetic Drift

Natural Selection

Natural Selection

Gene Flow

Mutations

POPULATION SIZE

MATING

VIABILITY

INTERACTION W/ OTHER POPS

DNA CHANGES

Genetic DriftRandom 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 DriftBottleneck 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 stableInitially 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)

Formerly adaptive form is no longer adaptive

Pop evolves toward newly adaptive form

MOST ADAPTIVE FORM

RANGE OF PHENOTYPES

RANGE OF PHENOTYPES

Modes of Selection Disruptive

(Diversifying)Intermediate form is

undesirable and decreases in #

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).