Directions of natural selection/ NATURAL SELECTION VARIATIONS 13

DIRECTIONS OF NATURAL SELECTION

Variation exists, due to:
1. Sexual reproduction  meiosis/recombination (p. 254)
2. Mutations

STABILIZING SELECTION

1. Eliminates extremes
2. Keeps pop. same, most common type
3. Examples: a. Mouse color b. Human birth weight

DIRECTIONAL SELECTION

1. Favors 1 extreme
2. Changes population
3. Examples: a. Ladybugs (p. 253)
b. Pesticide resistance (p. 254)
c. Peppered moth – (PROBLEM: staged experiments!)

DIVERSIFYING or DISRUPTIVE SELECTION

1. Both extremes favored
2. Changes population
3. Examples: Mice

HETEROZYGOTE SUPERIORITY/ADVANTAGE

1.AA = Normal, susceptible to malaria  die
2. Aa = Mild sickle, resist. malaria
3. aa = Sickle cell  die

OUR GENETIC FUTURE

1.  frequency of “bad alleles” in humans - MYOPIA - near-sighted
2. Man’s interference on selection; for example:
Overuse of antibiotics/pesticides 
 resistant microbes/pests (p. 254)
3. Loss of biodiversity due to some extinction

NATURAL SELECTION VARIATIONS

• HETEROZYGOTE SUPERIORITY/ADVANTAGE

• OUR GENETIC FUTURE