1. Selection acting on Populations

2. Selections Tool -allele – variations of a gene (blue/brown eyes)
-gene pool- all of the alleles in a population
-allelic frequency - the percentage of an allele in the gene pool
(when allele frequency changes, evolution is happening)
genetic equilibrium- is when allele frequencies do not change

3. Selection Types
Stabilizing- selection favors an average variation (size, color, etc) ex avg. sized colony spiders
600
500
400
300
200
100
# of spiders
size (inches)

5. Selection Types
Directional- selection favors one extreme variation. Ex. Elephant Size 60 50 40 30 20 10
# of elephants
height (feet)

7. Selection Types
Disruptive- selection favors two extreme variations. Ex. Black bellied seed crackers 60 50 40 30 20 10
# of birds
small beak large beak
Beak size

9. Frequency Dependant Selection
The fitness level of a given trait varies depending on how many organisms in the population have that trait.
Ex. Scale
Eating fish

11. Sexual Selection traits allow organisms to attract mates.
results in sexual dimorphism- differences between the sexes (size, color, etc)

12. Intrasexual Selection
Members of the same sex compete for mates **

13. Intersexual Selection
Member of one sex choose mates, usually based on particular traits, ornaments or behaviors
.**